Learn tool calling by reading a Python task agent on the OpenAI API: schemas, tools, the agent loop, and tool messages. Repo, quiz, and a real challenge.

Tool calling: build an AI task agent in Python | Tech Tips by Moh

Because `content` is always empty when tools are passed

Because a reply can be a tool call with no text, and the bot needs `tool_calls` to run it

Because the whole message is cheaper to send back

`definitions` is the list of schemas sent to the model; `by_name` maps each tool name to the Python function your program runs

`definitions` holds the tools allowed in this chat; `by_name` holds every tool in the file

`definitions` runs the tools; `by_name` describes them

`by_name` is sent to the model; `definitions` is only for tests

A tool message whose content is the error text from `require_status`, so the model can try again

A new user message asking for a valid status

The results come back in alphabetical order

Each tool message carries `tool_call_id`, equal to the `id` of the call it answers

The function name is repeated in the content

`require_due_date` turned tomorrow into the wrong year

The model skipped `get_todays_date` and guessed today, and `require_due_date` only proves a date is real

`tasks.json` stores dates in a different format

Tool calling: build an AI task agent in Python

<div class="course-slide cs-center">
  <p class="cs-kicker">Tip 11 · tool calling</p>
  <h2 class="cs-title cs-at-1-1">From <span class="cs-hl">answering</span> to <span class="cs-hl">doing</span></h2>
  <p class="cs-pill cs-at-4-8">The AI starts doing the work</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Picture an assistant</p>
  <h2 class="cs-title">It does not just answer. It <span class="cs-hl">acts</span>.</h2>
  <ol class="cs-steps">
    <li class="cs-at-0-6">Reads your message</li>
    <li class="cs-at-2">Checks your calendar</li>
    <li class="cs-at-3-1">Books the slot</li>
    <li class="cs-at-4-2">Updates the ticket</li>
    <li class="cs-at-5-5">Tells you it is done</li>
  </ol>
</div>

<div class="course-slide cs-center">
  <p class="cs-kicker">Real agents</p>
  <p class="cs-pill cs-at-0-4">Support bot: issues a refund</p>
  <p class="cs-pill cs-at-4">Coding agent: edits your files</p>
  <h2 class="cs-title cs-at-7-3">Under all of them, <span class="cs-hl">one loop</span></h2>
</div>

<div class="course-slide">
  <p class="cs-kicker">The loop</p>
  <ol class="cs-steps">
    <li>The <span class="cs-hl">model</span> decides which function should run</li>
    <li class="cs-at-2-5"><span class="cs-hl">Your code</span> runs it</li>
    <li class="cs-at-3-8">The result goes <span class="cs-hl">back</span> to the model</li>
  </ol>
  <h2 class="cs-title cs-at-5-9">That loop is <span class="cs-hl">tool calling</span></h2>
  <p class="cs-pill cs-at-9-2">Read it once, and bigger agents stop looking like magic</p>
  <p class="cs-pill cs-at-12-4"><span class="cs-hl">What AI engineer job posts mean by “experience building agents”</span></p>
</div>

<div class="course-slide cs-center">
  <p class="cs-kicker">Not one company</p>
  <h2 class="cs-title cs-at-2-1">Same loop, <span class="cs-hl">every major API</span></h2>
  <div class="cs-row">
    <p class="cs-pill cs-at-2-1">OpenAI · Anthropic · Google Gemini</p>
    <p class="cs-pill cs-at-7-6">Field names differ. The loop is the same.</p>
    <p class="cs-pill cs-at-10-2">This tip: the OpenAI API, runs as it is</p>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">A full code walkthrough</p>
  <h2 class="cs-title cs-at-0-1">Not theory. <span class="cs-hl">A real agent.</span></h2>
  <div class="cs-row">
    <span class="cs-chip cs-at-4-6">Plain Python</span>
    <span class="cs-chip cs-at-5-8">No framework</span>
  </div>
  <p class="cs-pill cs-at-7-1">You type plain English. The agent acts on your tasks:</p>
  <div class="cs-row">
    <span class="cs-chip cs-at-9-6">Reads</span>
    <span class="cs-chip cs-at-11-3">Adds</span>
    <span class="cs-chip cs-at-12-4">Changes</span>
    <span class="cs-chip cs-at-13-2">Deletes</span>
  </div>
  <p class="cs-pill cs-at-14-3"><span class="cs-hl">Real functions, writing to a real file</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">How we go</p>
  <ul class="cs-checks">
    <li>We open every file</li>
    <li class="cs-at-1-7">We read the lines that do the work</li>
  </ul>
  <h2 class="cs-title cs-at-3-4">By the end: how a <span class="cs-hl">sentence</span> becomes an <span class="cs-hl">action</span></h2>
  <p class="cs-pill cs-at-8"><span class="cs-hl">And you can build one yourself</span></p>
  <p class="cs-pill cs-at-9-5">All you need: read a Python function</p>
</div>

<div class="course-slide cs-center">
  <p class="cs-kicker">Watch for this</p>
  <h2 class="cs-title cs-at-6-4">Tomorrow became <span class="cs-bad">three years ago</span></h2>
  <p class="cs-pill cs-at-8-3">Every check in the code passed</p>
  <p class="cs-pill cs-at-14"><span class="cs-hl">Who makes the decisions inside an agent?</span></p>
</div>

<div class="course-slide cs-center">
  <p class="cs-kicker">What you leave with</p>
  <h2 class="cs-title cs-at-1-7">A working project for your <span class="cs-hl">résumé</span></h2>
  <p class="cs-pill cs-at-4-4">Rebuild it as you watch, or clone it and extend it</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">On your résumé</p>
  <div class="cs-card"><p class="cs-card-label">For example</p><p class="cs-quote">Built a tool-calling task agent in Python on the OpenAI API, with seven input-validated tools, a bounded agent loop, and in-session memory.</p></div>
  <div class="cs-card cs-card-accent cs-at-11-7"><p class="cs-card-label">And at the end</p><p class="cs-card-title">A real challenge: find the breaks, fix them, list the fixes too</p></div>
</div>

<div class="course-slide">
  <p class="cs-kicker">The code for this tip</p>
  <div class="cs-code cs-at-1-5">
    <div class="cs-code-bar"><span class="cs-code-path">GitHub</span></div>
    <pre class="cs-code-body">https://github.com/mmmohajer/tool_calling</pre>
  </div>
  <p class="cs-pill cs-at-7"><span class="cs-mono">mmmohajer</span>: three m’s, then mohajer</p>
  <div class="cs-row">
    <p class="cs-pill cs-at-12-9">Tip page: press Copy, or open the notes</p>
    <p class="cs-pill cs-at-18-4">YouTube: the link is in the description</p>
  </div>
</div>

<div class="course-slide">
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">terminal</span></div>
    <pre class="cs-code-body">git clone https://github.com/mmmohajer/tool_calling.git</pre>
  </div>
  <p class="cs-pill cs-at-1">Open it next to this video</p>
  <ol class="cs-steps">
    <li class="cs-at-7-1">Each file: what it is for</li>
    <li class="cs-at-9">Then what each important line does</li>
  </ol>
</div>

<div class="course-slide">
  <p class="cs-kicker">The one file that talks to the model</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">services/llm.py · lines 10–18</span></div>
    <pre class="cs-code-body cs-lines cs-from-10"><span class="cs-ln cs-focus-at-5-5"><span class="cs-key">class</span> Llm:</span>
<span class="cs-ln">    <span class="cs-key">def</span> __init__(self, chat_model: str = "gpt-4o"):</span>
<span class="cs-ln cs-focus-at-6-7">        api_key = os.getenv("OPEN_AI_API_KEY", "").strip()</span>
<span class="cs-ln cs-focus-at-6-7">        <span class="cs-key">if</span> not api_key:</span>
<span class="cs-ln cs-focus-at-6-7">            <span class="cs-key">raise</span> ValueError("OPEN_AI_API_KEY is not set")</span>
<span class="cs-ln cs-focus-at-10-8">        self._client = OpenAI(api_key=api_key)</span>
<span class="cs-ln">        self.chat_model = chat_model</span>
<span class="cs-ln"></span>
<span class="cs-ln cs-focus-at-13-2">    <span class="cs-key">def</span> generate_response(self, messages: list[dict], tools: list[dict] | None = None):</span></pre>
  </div>
  <p class="cs-pill cs-at-14-9">The only place that calls the API</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Parameter 1 · messages</p>
  <div class="cs-split">
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">services/llm.py · lines 18–29</span></div>
      <pre class="cs-code-body cs-lines cs-from-18"><span class="cs-ln cs-focus-at-0-5">    <span class="cs-key">def</span> generate_response(self, messages: list[dict], tools: list[dict] | None = None):</span>
<span class="cs-ln">        <span class="cs-key">if</span> not messages:</span>
<span class="cs-ln">            <span class="cs-key">raise</span> ValueError("messages are empty")</span>
<span class="cs-ln"></span>
<span class="cs-ln">        request: dict = {"model": self.chat_model, "messages": messages}</span>
<span class="cs-ln">        <span class="cs-key">if</span> tools:</span>
<span class="cs-ln">            request["tools"] = tools</span>
<span class="cs-ln">        response = self._client.chat.completions.create(**request)</span>
<span class="cs-ln">        message = response.choices[0].message</span>
<span class="cs-ln">        <span class="cs-key">if</span> not message.content and not message.tool_calls:</span>
<span class="cs-ln">            <span class="cs-key">raise</span> ValueError("model returned an empty response")</span>
<span class="cs-ln">        <span class="cs-key">return</span> message</span></pre>
    </div>
    <div class="cs-code cs-no-copy">
      <div class="cs-code-bar"><span class="cs-code-path">example · messages</span></div>
      <pre class="cs-code-body cs-lines cs-from-1 cs-focus-at-5-4"><span class="cs-ln">messages = [</span>
<span class="cs-ln cs-focus-at-12-9">    {"role": "system", "content": "You are a task agent. ..."},</span>
<span class="cs-ln cs-focus-at-15-7">    {"role": "user", "content": "Hello, how are you?"},</span>
<span class="cs-ln cs-focus-at-17-4">    {"role": "assistant", "content": "Hello! I'm here to help you with your tasks. ..."},</span>
<span class="cs-ln">]</span></pre>
    </div>
  </div>
  <p class="cs-pill cs-at-9-1">Each item: a <span class="cs-mono">role</span> and some <span class="cs-mono">content</span></p>
</div>

<div class="course-slide cs-center">
  <p class="cs-kicker">messages</p>
  <p class="cs-pill">Later: one more role, <span class="cs-mono">tool</span>, the result of a function</p>
  <p class="cs-pill cs-at-4-9">The model reads the whole list on every request</p>
  <h2 class="cs-title cs-at-7-9">Not in messages? The model <span class="cs-bad">does not know</span>.</h2>
</div>

<div class="course-slide">
  <p class="cs-kicker">Parameter 2 · tools</p>
  <div class="cs-split">
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">services/llm.py · lines 18–29</span></div>
      <pre class="cs-code-body cs-lines cs-from-18"><span class="cs-ln cs-focus-at-0">    <span class="cs-key">def</span> generate_response(self, messages: list[dict], tools: list[dict] | None = None):</span>
<span class="cs-ln">        <span class="cs-key">if</span> not messages:</span>
<span class="cs-ln">            <span class="cs-key">raise</span> ValueError("messages are empty")</span>
<span class="cs-ln"></span>
<span class="cs-ln">        request: dict = {"model": self.chat_model, "messages": messages}</span>
<span class="cs-ln cs-focus-at-4-7">        <span class="cs-key">if</span> tools:</span>
<span class="cs-ln cs-focus-at-4-7">            request["tools"] = tools</span>
<span class="cs-ln">        response = self._client.chat.completions.create(**request)</span>
<span class="cs-ln">        message = response.choices[0].message</span>
<span class="cs-ln">        <span class="cs-key">if</span> not message.content and not message.tool_calls:</span>
<span class="cs-ln">            <span class="cs-key">raise</span> ValueError("model returned an empty response")</span>
<span class="cs-ln">        <span class="cs-key">return</span> message</span></pre>
    </div>
    <div class="cs-code cs-no-copy">
      <div class="cs-code-bar"><span class="cs-code-path">example · tools</span></div>
      <pre class="cs-code-body cs-lines cs-from-1 cs-focus-at-4-7"><span class="cs-ln">tools = [</span>
<span class="cs-ln">    {</span>
<span class="cs-ln cs-focus-at-8-8">        "type": "function",</span>
<span class="cs-ln">        "function": {</span>
<span class="cs-ln cs-focus-at-10-5">            "name": "filter_tasks_by_status",</span>
<span class="cs-ln cs-focus-at-11-2">            "description": "Return tasks with this status.",</span>
<span class="cs-ln cs-focus-at-12-4">            "parameters": {</span>
<span class="cs-ln cs-focus-at-12-4">                "type": "object",</span>
<span class="cs-ln cs-focus-at-12-4">                "properties": {</span>
<span class="cs-ln cs-focus-at-12-4">                    "status": {"type": "string", "enum": ["todo", "in_progress", "done"]},</span>
<span class="cs-ln cs-focus-at-12-4">                },</span>
<span class="cs-ln cs-focus-at-12-4">                "required": ["status"],</span>
<span class="cs-ln cs-focus-at-12-4">            },</span>
<span class="cs-ln">        },</span>
<span class="cs-ln">    },</span>
<span class="cs-ln">]</span></pre>
    </div>
  </div>
  <p class="cs-pill cs-at-14-7">One schema per function, written as JSON Schema</p>
</div>

<div class="course-slide">
  <h2 class="cs-title">The model sees <span class="cs-hl">schemas</span>, never your Python</h2>
  <div class="cs-code cs-no-copy">
    <div class="cs-code-bar"><span class="cs-code-path">example · tools</span></div>
    <pre class="cs-code-body cs-lines cs-from-1 cs-focus-at-8-8"><span class="cs-ln">tools = [</span>
<span class="cs-ln">    {</span>
<span class="cs-ln">        "type": "function",</span>
<span class="cs-ln">        "function": {</span>
<span class="cs-ln cs-focus-at-4-5">            "name": "filter_tasks_by_status",</span>
<span class="cs-ln cs-focus-at-4-5">            "description": "Return tasks with this status.",</span>
<span class="cs-ln">            "parameters": {</span>
<span class="cs-ln">                "type": "object",</span>
<span class="cs-ln">                "properties": {</span>
<span class="cs-ln">                    "status": {"type": "string", "enum": ["todo", "in_progress", "done"]},</span>
<span class="cs-ln">                },</span>
<span class="cs-ln">                "required": ["status"],</span>
<span class="cs-ln">            },</span>
<span class="cs-ln">        },</span>
<span class="cs-ln">    },</span>
<span class="cs-ln">]</span></pre>
  </div>
  <p class="cs-pill cs-at-11-7">All 7 real schemas: in the agent folder</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Inside generate_response</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">services/llm.py · lines 18–29</span></div>
    <pre class="cs-code-body cs-lines cs-from-18"><span class="cs-ln">    <span class="cs-key">def</span> generate_response(self, messages: list[dict], tools: list[dict] | None = None):</span>
<span class="cs-ln cs-focus-at-0-7">        <span class="cs-key">if</span> not messages:</span>
<span class="cs-ln cs-focus-at-0-7">            <span class="cs-key">raise</span> ValueError("messages are empty")</span>
<span class="cs-ln"></span>
<span class="cs-ln cs-focus-at-6-3">        request: dict = {"model": self.chat_model, "messages": messages}</span>
<span class="cs-ln cs-focus-at-9-6">        <span class="cs-key">if</span> tools:</span>
<span class="cs-ln cs-focus-at-9-6">            request["tools"] = tools</span>
<span class="cs-ln cs-focus-at-15-9">        response = self._client.chat.completions.create(**request)</span>
<span class="cs-ln cs-focus-at-17-9">        message = response.choices[0].message</span>
<span class="cs-ln">        <span class="cs-key">if</span> not message.content and not message.tool_calls:</span>
<span class="cs-ln">            <span class="cs-key">raise</span> ValueError("model returned an empty response")</span>
<span class="cs-ln">        <span class="cs-key">return</span> message</span></pre>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">What it returns</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">services/llm.py · lines 18–29</span></div>
    <pre class="cs-code-body cs-lines cs-from-18"><span class="cs-ln">    <span class="cs-key">def</span> generate_response(self, messages: list[dict], tools: list[dict] | None = None):</span>
<span class="cs-ln">        <span class="cs-key">if</span> not messages:</span>
<span class="cs-ln">            <span class="cs-key">raise</span> ValueError("messages are empty")</span>
<span class="cs-ln"></span>
<span class="cs-ln">        request: dict = {"model": self.chat_model, "messages": messages}</span>
<span class="cs-ln">        <span class="cs-key">if</span> tools:</span>
<span class="cs-ln">            request["tools"] = tools</span>
<span class="cs-ln">        response = self._client.chat.completions.create(**request)</span>
<span class="cs-ln cs-focus-at-5-6">        message = response.choices[0].message</span>
<span class="cs-ln cs-focus-at-10-8">        <span class="cs-key">if</span> not message.content and not message.tool_calls:</span>
<span class="cs-ln cs-focus-at-10-8">            <span class="cs-key">raise</span> ValueError("model returned an empty response")</span>
<span class="cs-ln cs-focus-at-0">        <span class="cs-key">return</span> message</span></pre>
  </div>
  <p class="cs-pill cs-at-1-4">RAG tip: only the text. Here: the whole message</p>
  <p class="cs-pill cs-at-8-9"><span class="cs-hl">A message can carry tool calls instead of text</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Where we are</p>
  <ul class="cs-checks">
    <li>Tool calls are handled in the bot, after every tool</li>
    <li class="cs-at-7">The API side: done</li>
  </ul>
  <h2 class="cs-title cs-at-9-4">Before the agent: <span class="cs-hl">the data</span></h2>
</div>

<div class="course-slide">
  <p class="cs-kicker">The store</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">tasks.json · lines 1–23</span></div>
    <pre class="cs-code-body cs-lines cs-from-1 cs-focus-at-2-1"><span class="cs-ln">[</span>
<span class="cs-ln">  {</span>
<span class="cs-ln cs-focus-at-4-6">    "id": 1,</span>
<span class="cs-ln cs-focus-at-4-6">    "title": "Buy groceries",</span>
<span class="cs-ln cs-focus-at-4-6">    "description": "Milk, eggs, bread, and coffee.",</span>
<span class="cs-ln cs-focus-at-4-6 cs-focus-at-9-7">    "status": "todo",</span>
<span class="cs-ln cs-focus-at-4-6 cs-focus-at-14">    "due_date": "2026-11-05"</span>
<span class="cs-ln">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln">    "id": 2,</span>
<span class="cs-ln">    "title": "Write the tutorial outline",</span>
<span class="cs-ln">    "description": "List the sections for the tool-calling lesson.",</span>
<span class="cs-ln">    "status": "in_progress",</span>
<span class="cs-ln">    "due_date": "2026-11-03"</span>
<span class="cs-ln">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln">    "id": 3,</span>
<span class="cs-ln">    "title": "Call the dentist",</span>
<span class="cs-ln">    "description": "Schedule a cleaning for next month.",</span>
<span class="cs-ln">    "status": "done",</span>
<span class="cs-ln">    "due_date": "2026-10-28"</span>
<span class="cs-ln">  }</span>
<span class="cs-ln">]</span></pre>
  </div>
  <div class="cs-row">
    <span class="cs-chip cs-at-11-3">todo</span>
    <span class="cs-chip cs-at-12">in_progress</span>
    <span class="cs-chip cs-at-12-8">done</span>
    <span class="cs-chip cs-at-15-1">YYYY-MM-DD</span>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">Three starting tasks</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">tasks.json · lines 1–23</span></div>
    <pre class="cs-code-body cs-lines cs-from-1"><span class="cs-ln">[</span>
<span class="cs-ln cs-focus-at-2-3">  {</span>
<span class="cs-ln cs-focus-at-2-3">    "id": 1,</span>
<span class="cs-ln cs-focus-at-2-3">    "title": "Buy groceries",</span>
<span class="cs-ln cs-focus-at-2-3">    "description": "Milk, eggs, bread, and coffee.",</span>
<span class="cs-ln cs-focus-at-2-3">    "status": "todo",</span>
<span class="cs-ln cs-focus-at-2-3">    "due_date": "2026-11-05"</span>
<span class="cs-ln cs-focus-at-2-3">  },</span>
<span class="cs-ln cs-focus-at-3-4">  {</span>
<span class="cs-ln cs-focus-at-3-4">    "id": 2,</span>
<span class="cs-ln cs-focus-at-3-4">    "title": "Write the tutorial outline",</span>
<span class="cs-ln cs-focus-at-3-4">    "description": "List the sections for the tool-calling lesson.",</span>
<span class="cs-ln cs-focus-at-3-4">    "status": "in_progress",</span>
<span class="cs-ln cs-focus-at-3-4">    "due_date": "2026-11-03"</span>
<span class="cs-ln cs-focus-at-3-4">  },</span>
<span class="cs-ln cs-focus-at-5-1">  {</span>
<span class="cs-ln cs-focus-at-5-1">    "id": 3,</span>
<span class="cs-ln cs-focus-at-5-1">    "title": "Call the dentist",</span>
<span class="cs-ln cs-focus-at-5-1">    "description": "Schedule a cleaning for next month.",</span>
<span class="cs-ln cs-focus-at-5-1">    "status": "done",</span>
<span class="cs-ln cs-focus-at-5-1">    "due_date": "2026-10-28"</span>
<span class="cs-ln cs-focus-at-5-1">  }</span>
<span class="cs-ln">]</span></pre>
  </div>
  <p class="cs-pill cs-at-6-2">Personal use: a file is enough</p>
  <p class="cs-pill cs-at-11-5"><span class="cs-hl">A real app: the same rows in a permanent database</span></p>
</div>

<div class="course-slide cs-center">
  <p class="cs-kicker">agent/tools.py</p>
  <h2 class="cs-title cs-at-6-2">The agent’s <span class="cs-hl">hands</span></h2>
  <p class="cs-pill cs-at-7-9">It holds the real schemas for the tools parameter</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Each tool, two halves</p>
  <div class="cs-grid cs-cols-2">
    <div class="cs-card cs-at-2"><p class="cs-card-label">Schema</p><p class="cs-card-title">What the model reads: a name, a description, the arguments</p></div>
    <div class="cs-card cs-card-accent cs-at-7-6"><p class="cs-card-label">Function</p><p class="cs-card-title">The Python that actually runs</p></div>
  </div>
  <p class="cs-pill cs-at-10-5">7 tools, then the loop in the bot that runs them</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">How we read each tool</p>
  <ol class="cs-steps">
    <li class="cs-at-1-7">The schema first</li>
    <li class="cs-at-2-7">Then the function</li>
    <li class="cs-at-4-4">A helper? Open <span class="cs-mono">agent/helpers.py</span>, then come back</li>
  </ol>
</div>

<div class="course-slide">
  <p class="cs-kicker">Tool 1 · get_todays_date</p>
  <div class="cs-split">
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 107–115</span></div>
      <pre class="cs-code-body cs-lines cs-from-107"><span class="cs-ln">definitions = [</span>
<span class="cs-ln">    {</span>
<span class="cs-ln">        "type": "function",</span>
<span class="cs-ln">        "function": {</span>
<span class="cs-ln cs-focus-at-0">            "name": "get_todays_date",</span>
<span class="cs-ln">            "description": "Return today's date as YYYY-MM-DD.",</span>
<span class="cs-ln cs-focus-at-3-7">            "parameters": {"type": "object", "properties": {}},</span>
<span class="cs-ln">        },</span>
<span class="cs-ln">    },</span></pre>
    </div>
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 15–17</span></div>
      <pre class="cs-code-body cs-lines cs-from-15"><span class="cs-ln"><span class="cs-key">def</span> get_todays_date() -&gt; str:</span>
<span class="cs-ln">    """Return today's date as YYYY-MM-DD."""</span>
<span class="cs-ln cs-focus-at-5-5">    <span class="cs-key">return</span> date.today().isoformat()</span></pre>
    </div>
  </div>
</div>

<div class="course-slide cs-center">
  <p class="cs-kicker">Why it matters</p>
  <h2 class="cs-title cs-at-2-4">A model has <span class="cs-hl">no clock</span></h2>
  <p class="cs-pill cs-at-3-7">Without this tool, “tomorrow” is a guess</p>
  <p class="cs-pill cs-at-7-6"><span class="cs-hl">The test at the end shows that guess</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Tool 2 · create_task</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 116–132</span></div>
    <pre class="cs-code-body cs-lines cs-from-116"><span class="cs-ln">    {</span>
<span class="cs-ln">        "type": "function",</span>
<span class="cs-ln">        "function": {</span>
<span class="cs-ln cs-focus-at-0">            "name": "create_task",</span>
<span class="cs-ln">            "description": "Add a task. The id is assigned automatically.",</span>
<span class="cs-ln">            "parameters": {</span>
<span class="cs-ln">                "type": "object",</span>
<span class="cs-ln">                "properties": {</span>
<span class="cs-ln cs-focus-at-6-9">                    "title": {"type": "string"},</span>
<span class="cs-ln cs-focus-at-6-9">                    "description": {"type": "string"},</span>
<span class="cs-ln cs-focus-at-6-9 cs-focus-at-10-7">                    "status": {"type": "string", "enum": ["todo", "in_progress", "done"]},</span>
<span class="cs-ln cs-focus-at-6-9 cs-focus-at-12-9">                    "due_date": {"type": "string", "description": "YYYY-MM-DD"},</span>
<span class="cs-ln">                },</span>
<span class="cs-ln cs-focus-at-5-2">                "required": ["title", "description", "status", "due_date"],</span>
<span class="cs-ln">            },</span>
<span class="cs-ln">        },</span>
<span class="cs-ln">    },</span></pre>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">create_task · load_tasks</p>
  <div class="cs-split">
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 20–32</span></div>
      <pre class="cs-code-body cs-lines cs-from-20"><span class="cs-ln"><span class="cs-key">def</span> create_task(title: str, description: str, status: str, due_date: str) -&gt; dict:</span>
<span class="cs-ln">    """Add a task. Its id is one greater than the id of the last task."""</span>
<span class="cs-ln cs-focus-at-2">    tasks = load_tasks()</span>
<span class="cs-ln">    task = {</span>
<span class="cs-ln">        "id": 1 if not tasks else require_task_id(tasks[-1]["id"], "last task") + 1,</span>
<span class="cs-ln">        "title": require_text(title, "title"),</span>
<span class="cs-ln">        "description": require_text(description, "description"),</span>
<span class="cs-ln">        "status": require_status(status),</span>
<span class="cs-ln">        "due_date": require_due_date(due_date),</span>
<span class="cs-ln">    }</span>
<span class="cs-ln">    tasks.append(task)</span>
<span class="cs-ln">    save_tasks(tasks)</span>
<span class="cs-ln">    <span class="cs-key">return</span> task</span></pre>
    </div>
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/helpers.py · lines 10–19</span></div>
      <pre class="cs-code-body cs-lines cs-from-10"><span class="cs-ln cs-focus-at-4-6"><span class="cs-key">def</span> load_tasks() -&gt; list[dict]:</span>
<span class="cs-ln cs-focus-at-10-2">    <span class="cs-key">if</span> not _TASKS_PATH.exists():</span>
<span class="cs-ln cs-focus-at-10-2">        <span class="cs-key">return</span> []</span>
<span class="cs-ln">    text = _TASKS_PATH.read_text().strip()</span>
<span class="cs-ln cs-focus-at-10-2">    <span class="cs-key">if</span> not text:</span>
<span class="cs-ln cs-focus-at-10-2">        <span class="cs-key">return</span> []</span>
<span class="cs-ln cs-focus-at-14">    tasks = json.loads(text)</span>
<span class="cs-ln cs-focus-at-16">    <span class="cs-key">if</span> not isinstance(tasks, list):</span>
<span class="cs-ln cs-focus-at-16">        <span class="cs-key">raise</span> ValueError("tasks.json must be an array")</span>
<span class="cs-ln">    <span class="cs-key">return</span> tasks</span></pre>
    </div>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">create_task · one checked field at a time</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 20–32</span></div>
    <pre class="cs-code-body cs-lines cs-from-20"><span class="cs-ln"><span class="cs-key">def</span> create_task(title: str, description: str, status: str, due_date: str) -&gt; dict:</span>
<span class="cs-ln">    """Add a task. Its id is one greater than the id of the last task."""</span>
<span class="cs-ln">    tasks = load_tasks()</span>
<span class="cs-ln cs-focus-at-2-2">    task = {</span>
<span class="cs-ln cs-focus-at-2-2 cs-focus-at-5-7">        "id": 1 if not tasks else require_task_id(tasks[-1]["id"], "last task") + 1,</span>
<span class="cs-ln cs-focus-at-2-2">        "title": require_text(title, "title"),</span>
<span class="cs-ln cs-focus-at-2-2">        "description": require_text(description, "description"),</span>
<span class="cs-ln cs-focus-at-2-2">        "status": require_status(status),</span>
<span class="cs-ln cs-focus-at-2-2">        "due_date": require_due_date(due_date),</span>
<span class="cs-ln cs-focus-at-2-2">    }</span>
<span class="cs-ln">    tasks.append(task)</span>
<span class="cs-ln">    save_tasks(tasks)</span>
<span class="cs-ln">    <span class="cs-key">return</span> task</span></pre>
  </div>
  <p class="cs-pill cs-at-7-8">Empty list: id <span class="cs-mono">1</span></p>
  <p class="cs-pill cs-at-11-7">Otherwise: the last task’s id + 1</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">create_task · the checks</p>
  <div class="cs-split">
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 20–32</span></div>
      <pre class="cs-code-body cs-lines cs-from-20"><span class="cs-ln"><span class="cs-key">def</span> create_task(title: str, description: str, status: str, due_date: str) -&gt; dict:</span>
<span class="cs-ln">    """Add a task. Its id is one greater than the id of the last task."""</span>
<span class="cs-ln">    tasks = load_tasks()</span>
<span class="cs-ln">    task = {</span>
<span class="cs-ln cs-focus-at-0-5">        "id": 1 if not tasks else require_task_id(tasks[-1]["id"], "last task") + 1,</span>
<span class="cs-ln cs-focus-at-9-4">        "title": require_text(title, "title"),</span>
<span class="cs-ln cs-focus-at-9-4">        "description": require_text(description, "description"),</span>
<span class="cs-ln">        "status": require_status(status),</span>
<span class="cs-ln">        "due_date": require_due_date(due_date),</span>
<span class="cs-ln">    }</span>
<span class="cs-ln">    tasks.append(task)</span>
<span class="cs-ln">    save_tasks(tasks)</span>
<span class="cs-ln">    <span class="cs-key">return</span> task</span></pre>
    </div>
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/helpers.py · lines 33–68</span></div>
      <pre class="cs-code-body cs-lines cs-from-33"><span class="cs-ln cs-focus-at-9-4"><span class="cs-key">def</span> require_text(value: str, name: str) -&gt; str:</span>
<span class="cs-ln cs-focus-at-9-4 cs-focus-at-12-3">    <span class="cs-key">if</span> not isinstance(value, str) or value.strip() == "" or value != value.strip():</span>
<span class="cs-ln cs-focus-at-9-4">        <span class="cs-key">raise</span> ValueError(f"{name} must be a non-empty string")</span>
<span class="cs-ln cs-focus-at-9-4">    <span class="cs-key">return</span> value</span>
<span class="cs-ln cs-gap">  # 28 lines</span>
<span class="cs-ln cs-from-65 cs-focus-at-0-5"><span class="cs-key">def</span> require_task_id(value: int, name: str) -&gt; int:</span>
<span class="cs-ln cs-focus-at-0-5 cs-focus-at-4-9">    <span class="cs-key">if</span> isinstance(value, bool) or not isinstance(value, int):</span>
<span class="cs-ln cs-focus-at-0-5">        <span class="cs-key">raise</span> ValueError(f"{name} must be an integer")</span>
<span class="cs-ln cs-focus-at-0-5">    <span class="cs-key">return</span> value</span></pre>
    </div>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">create_task · status and date</p>
  <div class="cs-split">
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 20–32</span></div>
      <pre class="cs-code-body cs-lines cs-from-20"><span class="cs-ln"><span class="cs-key">def</span> create_task(title: str, description: str, status: str, due_date: str) -&gt; dict:</span>
<span class="cs-ln">    """Add a task. Its id is one greater than the id of the last task."""</span>
<span class="cs-ln">    tasks = load_tasks()</span>
<span class="cs-ln">    task = {</span>
<span class="cs-ln">        "id": 1 if not tasks else require_task_id(tasks[-1]["id"], "last task") + 1,</span>
<span class="cs-ln">        "title": require_text(title, "title"),</span>
<span class="cs-ln">        "description": require_text(description, "description"),</span>
<span class="cs-ln cs-focus-at-0-8">        "status": require_status(status),</span>
<span class="cs-ln cs-focus-at-7">        "due_date": require_due_date(due_date),</span>
<span class="cs-ln">    }</span>
<span class="cs-ln">    tasks.append(task)</span>
<span class="cs-ln">    save_tasks(tasks)</span>
<span class="cs-ln">    <span class="cs-key">return</span> task</span></pre>
    </div>
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/helpers.py · lines 39–53</span></div>
      <pre class="cs-code-body cs-lines cs-from-39"><span class="cs-ln cs-focus-at-0-8"><span class="cs-key">def</span> require_status(value: str) -&gt; str:</span>
<span class="cs-ln cs-focus-at-0-8">    <span class="cs-key">if</span> value not in _STATUSES:</span>
<span class="cs-ln cs-focus-at-0-8 cs-focus-at-4-4">        allowed = ", ".join(sorted(_STATUSES))</span>
<span class="cs-ln cs-focus-at-0-8 cs-focus-at-4-4">        <span class="cs-key">raise</span> ValueError(f"status must be one of: {allowed}")</span>
<span class="cs-ln cs-focus-at-0-8">    <span class="cs-key">return</span> value</span>
<span class="cs-ln"></span>
<span class="cs-ln"></span>
<span class="cs-ln cs-focus-at-7"><span class="cs-key">def</span> require_due_date(value: str) -&gt; str:</span>
<span class="cs-ln cs-focus-at-7">    <span class="cs-key">if</span> not isinstance(value, str):</span>
<span class="cs-ln cs-focus-at-7">        <span class="cs-key">raise</span> ValueError("due_date must be a YYYY-MM-DD string")</span>
<span class="cs-ln cs-focus-at-7 cs-focus-at-11-4">    <span class="cs-key">try</span>:</span>
<span class="cs-ln cs-focus-at-7 cs-focus-at-11-4 cs-focus-at-13-4">        date.fromisoformat(value)</span>
<span class="cs-ln cs-focus-at-7">    <span class="cs-key">except</span> ValueError:</span>
<span class="cs-ln cs-focus-at-7">        <span class="cs-key">raise</span> ValueError("due_date must be a YYYY-MM-DD string") from None</span>
<span class="cs-ln cs-focus-at-7">    <span class="cs-key">return</span> value</span></pre>
    </div>
  </div>
  <p class="cs-pill cs-at-18-3"><span class="cs-bad">A date from the wrong year still passes</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">create_task · save</p>
  <div class="cs-split">
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 20–32</span></div>
      <pre class="cs-code-body cs-lines cs-from-20"><span class="cs-ln"><span class="cs-key">def</span> create_task(title: str, description: str, status: str, due_date: str) -&gt; dict:</span>
<span class="cs-ln">    """Add a task. Its id is one greater than the id of the last task."""</span>
<span class="cs-ln">    tasks = load_tasks()</span>
<span class="cs-ln">    task = {</span>
<span class="cs-ln">        "id": 1 if not tasks else require_task_id(tasks[-1]["id"], "last task") + 1,</span>
<span class="cs-ln">        "title": require_text(title, "title"),</span>
<span class="cs-ln">        "description": require_text(description, "description"),</span>
<span class="cs-ln">        "status": require_status(status),</span>
<span class="cs-ln">        "due_date": require_due_date(due_date),</span>
<span class="cs-ln">    }</span>
<span class="cs-ln cs-focus-at-2-5">    tasks.append(task)</span>
<span class="cs-ln cs-focus-at-4">    save_tasks(tasks)</span>
<span class="cs-ln cs-focus-at-9-4">    <span class="cs-key">return</span> task</span></pre>
    </div>
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/helpers.py · lines 22–23</span></div>
      <pre class="cs-code-body cs-lines cs-from-22"><span class="cs-ln"><span class="cs-key">def</span> save_tasks(tasks: list[dict]) -&gt; None:</span>
<span class="cs-ln cs-focus-at-4">    _TASKS_PATH.write_text(json.dumps(tasks, indent=2) + "\n")</span></pre>
    </div>
  </div>
  <p class="cs-pill cs-at-7-2"><span class="cs-mono">indent=2</span>: the whole list, neatly indented</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">When a check fails · call_tool</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/helpers.py · lines 88–98</span></div>
    <pre class="cs-code-body cs-lines cs-from-88"><span class="cs-ln cs-focus-at-3-4"><span class="cs-key">def</span> call_tool(call) -&gt; str:</span>
<span class="cs-ln cs-focus-at-16-4">    <span class="cs-key">from</span> agent.tools import by_name</span>
<span class="cs-ln"></span>
<span class="cs-ln">    <span class="cs-key">try</span>:</span>
<span class="cs-ln cs-focus-at-9-1">        arguments = json.loads(call.function.arguments or "{}")</span>
<span class="cs-ln cs-focus-at-13-9">        <span class="cs-key">if</span> not isinstance(arguments, dict):</span>
<span class="cs-ln cs-focus-at-13-9">            <span class="cs-key">raise</span> ValueError("tool arguments must be an object")</span>
<span class="cs-ln cs-focus-at-16-4 cs-focus-at-21-7">        result = by_name[call.function.name](**arguments)</span>
<span class="cs-ln">    <span class="cs-key">except</span> (ValueError, TypeError, KeyError, json.JSONDecodeError) as exc:</span>
<span class="cs-ln">        <span class="cs-key">return</span> str(exc)</span>
<span class="cs-ln">    <span class="cs-key">return</span> json.dumps(result)</span></pre>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">call_tool does not crash</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/helpers.py · lines 88–98</span></div>
    <pre class="cs-code-body cs-lines cs-from-88"><span class="cs-ln"><span class="cs-key">def</span> call_tool(call) -&gt; str:</span>
<span class="cs-ln">    <span class="cs-key">from</span> agent.tools import by_name</span>
<span class="cs-ln"></span>
<span class="cs-ln">    <span class="cs-key">try</span>:</span>
<span class="cs-ln">        arguments = json.loads(call.function.arguments or "{}")</span>
<span class="cs-ln">        <span class="cs-key">if</span> not isinstance(arguments, dict):</span>
<span class="cs-ln">            <span class="cs-key">raise</span> ValueError("tool arguments must be an object")</span>
<span class="cs-ln">        result = by_name[call.function.name](**arguments)</span>
<span class="cs-ln cs-focus-at-0">    <span class="cs-key">except</span> (ValueError, TypeError, KeyError, json.JSONDecodeError) as exc:</span>
<span class="cs-ln cs-focus-at-7-7">        <span class="cs-key">return</span> str(exc)</span>
<span class="cs-ln cs-focus-at-15-3">    <span class="cs-key">return</span> json.dumps(result)</span></pre>
  </div>
  <p class="cs-pill cs-at-10"><span class="cs-hl">The error is the tool result. The model reads it and can try again.</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Tool 3 · filter_tasks_by_text</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 133–149</span></div>
    <pre class="cs-code-body cs-lines cs-from-133"><span class="cs-ln">    {</span>
<span class="cs-ln">        "type": "function",</span>
<span class="cs-ln">        "function": {</span>
<span class="cs-ln cs-focus-at-1-9">            "name": "filter_tasks_by_text",</span>
<span class="cs-ln">            "description": (</span>
<span class="cs-ln">                "Find tasks whose title or description matches a regular expression. "</span>
<span class="cs-ln">                "Each task includes its id."</span>
<span class="cs-ln">            ),</span>
<span class="cs-ln">            "parameters": {</span>
<span class="cs-ln">                "type": "object",</span>
<span class="cs-ln">                "properties": {</span>
<span class="cs-ln cs-focus-at-5 cs-focus-at-8-3">                    "pattern": {"type": "string", "description": "Regular expression."},</span>
<span class="cs-ln">                },</span>
<span class="cs-ln cs-focus-at-8-3">                "required": ["pattern"],</span>
<span class="cs-ln">            },</span>
<span class="cs-ln">        },</span>
<span class="cs-ln">    },</span></pre>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">filter_tasks_by_text</p>
  <div class="cs-split">
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/helpers.py · lines 56–62</span></div>
      <pre class="cs-code-body cs-lines cs-from-56"><span class="cs-ln"><span class="cs-key">def</span> require_pattern(value: str) -&gt; re.Pattern[str]:</span>
<span class="cs-ln cs-focus-at-0">    <span class="cs-key">if</span> not isinstance(value, str) or value.strip() == "":</span>
<span class="cs-ln cs-focus-at-0">        <span class="cs-key">raise</span> ValueError("pattern must be a non-empty regular expression")</span>
<span class="cs-ln cs-focus-at-2-4">    <span class="cs-key">try</span>:</span>
<span class="cs-ln cs-focus-at-2-4">        <span class="cs-key">return</span> re.compile(value)</span>
<span class="cs-ln cs-focus-at-2-4">    <span class="cs-key">except</span> re.error as exc:</span>
<span class="cs-ln cs-focus-at-2-4">        <span class="cs-key">raise</span> ValueError(f"pattern is not a valid regular expression ({exc})") from exc</span></pre>
    </div>
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 35–43</span></div>
      <pre class="cs-code-body cs-lines cs-from-35"><span class="cs-ln"><span class="cs-key">def</span> filter_tasks_by_text(pattern: str) -&gt; list[dict]:</span>
<span class="cs-ln">    """Return tasks whose title or description matches this regular expression."""</span>
<span class="cs-ln cs-focus-at-0">    compiled = require_pattern(pattern)</span>
<span class="cs-ln cs-focus-at-4-7">    <span class="cs-key">return</span> [</span>
<span class="cs-ln cs-focus-at-4-7">        task</span>
<span class="cs-ln cs-focus-at-4-7">        <span class="cs-key">for</span> task in load_tasks()</span>
<span class="cs-ln cs-focus-at-4-7">        <span class="cs-key">if</span> compiled.search(str(task.get("title", "")))</span>
<span class="cs-ln cs-focus-at-4-7">        or compiled.search(str(task.get("description", "")))</span>
<span class="cs-ln cs-focus-at-4-7">    ]</span></pre>
    </div>
  </div>
  <p class="cs-pill cs-at-8-2">Regex: a detail of this tool, not part of the loop</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Tools 4 and 5 · one exact match each</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 46–55</span></div>
    <pre class="cs-code-body cs-lines cs-from-46"><span class="cs-ln cs-focus-at-5-6"><span class="cs-key">def</span> filter_tasks_by_due_date(due_date: str) -&gt; list[dict]:</span>
<span class="cs-ln cs-focus-at-5-6">    """Return tasks whose due date is exactly this date."""</span>
<span class="cs-ln cs-focus-at-5-6 cs-focus-at-7-1">    expected = require_due_date(due_date)</span>
<span class="cs-ln cs-focus-at-5-6 cs-focus-at-9">    <span class="cs-key">return</span> [task for task in load_tasks() if task.get("due_date") == expected]</span>
<span class="cs-ln"></span>
<span class="cs-ln"></span>
<span class="cs-ln cs-focus-at-12-3"><span class="cs-key">def</span> filter_tasks_by_status(status: str) -&gt; list[dict]:</span>
<span class="cs-ln cs-focus-at-12-3">    """Return tasks with this status."""</span>
<span class="cs-ln cs-focus-at-12-3 cs-focus-at-13-9">    expected = require_status(status)</span>
<span class="cs-ln cs-focus-at-12-3 cs-focus-at-16-1">    <span class="cs-key">return</span> [task for task in load_tasks() if task.get("status") == expected]</span></pre>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">Tool 6 · update_task</p>
  <div class="cs-split">
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 178–195</span></div>
      <pre class="cs-code-body cs-lines cs-from-178"><span class="cs-ln">    {</span>
<span class="cs-ln">        "type": "function",</span>
<span class="cs-ln">        "function": {</span>
<span class="cs-ln">            "name": "update_task",</span>
<span class="cs-ln">            "description": "Change a task by id. Find the id with filter_tasks_by_text when the user did not give one.",</span>
<span class="cs-ln">            "parameters": {</span>
<span class="cs-ln">                "type": "object",</span>
<span class="cs-ln">                "properties": {</span>
<span class="cs-ln cs-focus-at-1-8">                    "task_id": {"type": "integer"},</span>
<span class="cs-ln cs-focus-at-7-7">                    "title": {"type": "string"},</span>
<span class="cs-ln cs-focus-at-7-7">                    "description": {"type": "string"},</span>
<span class="cs-ln cs-focus-at-7-7">                    "status": {"type": "string", "enum": ["todo", "in_progress", "done"]},</span>
<span class="cs-ln cs-focus-at-7-7">                    "due_date": {"type": "string", "description": "YYYY-MM-DD"},</span>
<span class="cs-ln">                },</span>
<span class="cs-ln cs-focus-at-1-8">                "required": ["task_id"],</span>
<span class="cs-ln">            },</span>
<span class="cs-ln">        },</span>
<span class="cs-ln">    },</span></pre>
    </div>
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 58–82</span></div>
      <pre class="cs-code-body cs-lines cs-from-58"><span class="cs-ln"><span class="cs-key">def</span> update_task(</span>
<span class="cs-ln">    task_id: int,</span>
<span class="cs-ln">    title: str | None = None,</span>
<span class="cs-ln">    description: str | None = None,</span>
<span class="cs-ln">    status: str | None = None,</span>
<span class="cs-ln">    due_date: str | None = None,</span>
<span class="cs-ln">) -&gt; dict:</span>
<span class="cs-ln">    """Change the given fields of the task with this id."""</span>
<span class="cs-ln cs-focus-at-9-6">    changes = {}</span>
<span class="cs-ln cs-focus-at-9-6">    <span class="cs-key">if</span> title is not None:</span>
<span class="cs-ln cs-focus-at-9-6">        changes["title"] = require_text(title, "title")</span>
<span class="cs-ln cs-focus-at-9-6">    <span class="cs-key">if</span> description is not None:</span>
<span class="cs-ln cs-focus-at-9-6">        changes["description"] = require_text(description, "description")</span>
<span class="cs-ln cs-focus-at-9-6">    <span class="cs-key">if</span> status is not None:</span>
<span class="cs-ln cs-focus-at-9-6">        changes["status"] = require_status(status)</span>
<span class="cs-ln cs-focus-at-9-6">    <span class="cs-key">if</span> due_date is not None:</span>
<span class="cs-ln cs-focus-at-9-6">        changes["due_date"] = require_due_date(due_date)</span>
<span class="cs-ln cs-focus-at-15">    <span class="cs-key">if</span> not changes:</span>
<span class="cs-ln cs-focus-at-15">        <span class="cs-key">raise</span> ValueError("update needs at least one field to change")</span>
<span class="cs-ln"></span>
<span class="cs-ln cs-focus-at-22">    tasks = load_tasks()</span>
<span class="cs-ln cs-focus-at-22">    task = find_task(tasks, require_task_id(task_id, "task_id"))</span>
<span class="cs-ln">    task.update(changes)</span>
<span class="cs-ln">    save_tasks(tasks)</span>
<span class="cs-ln">    <span class="cs-key">return</span> task</span></pre>
    </div>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">update_task · find_task</p>
  <div class="cs-split">
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/helpers.py · lines 26–30</span></div>
      <pre class="cs-code-body cs-lines cs-from-26"><span class="cs-ln cs-focus-at-2-4"><span class="cs-key">def</span> find_task(tasks: list[dict], task_id: int) -&gt; dict:</span>
<span class="cs-ln cs-focus-at-2-4">    <span class="cs-key">for</span> task in tasks:</span>
<span class="cs-ln cs-focus-at-2-4">        <span class="cs-key">if</span> task.get("id") == task_id:</span>
<span class="cs-ln cs-focus-at-2-4">            <span class="cs-key">return</span> task</span>
<span class="cs-ln cs-focus-at-5-3">    <span class="cs-key">raise</span> ValueError(f"task {task_id} was not found")</span></pre>
    </div>
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 78–82</span></div>
      <pre class="cs-code-body cs-lines cs-from-78"><span class="cs-ln">    tasks = load_tasks()</span>
<span class="cs-ln cs-focus-at-0">    task = find_task(tasks, require_task_id(task_id, "task_id"))</span>
<span class="cs-ln cs-focus-at-11-4">    task.update(changes)</span>
<span class="cs-ln cs-focus-at-12-7">    save_tasks(tasks)</span>
<span class="cs-ln cs-focus-at-14-2">    <span class="cs-key">return</span> task</span></pre>
    </div>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">Tool 7 · delete_task</p>
  <div class="cs-split">
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 196–209</span></div>
      <pre class="cs-code-body cs-lines cs-from-196"><span class="cs-ln">    {</span>
<span class="cs-ln">        "type": "function",</span>
<span class="cs-ln">        "function": {</span>
<span class="cs-ln">            "name": "delete_task",</span>
<span class="cs-ln">            "description": "Delete a task by id. Find the id with filter_tasks_by_text when the user did not give one.",</span>
<span class="cs-ln">            "parameters": {</span>
<span class="cs-ln">                "type": "object",</span>
<span class="cs-ln">                "properties": {</span>
<span class="cs-ln cs-focus-at-0-4">                    "task_id": {"type": "integer"},</span>
<span class="cs-ln">                },</span>
<span class="cs-ln cs-focus-at-0-4">                "required": ["task_id"],</span>
<span class="cs-ln">            },</span>
<span class="cs-ln">        },</span>
<span class="cs-ln">    },</span></pre>
    </div>
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 85–94</span></div>
      <pre class="cs-code-body cs-lines cs-from-85"><span class="cs-ln"><span class="cs-key">def</span> delete_task(task_id: int) -&gt; dict:</span>
<span class="cs-ln">    """Remove the task with this id and return it."""</span>
<span class="cs-ln cs-focus-at-2-8">    tasks = load_tasks()</span>
<span class="cs-ln cs-focus-at-2-8">    expected = require_task_id(task_id, "task_id")</span>
<span class="cs-ln cs-focus-at-5-7">    <span class="cs-key">for</span> index, task in enumerate(tasks):</span>
<span class="cs-ln cs-focus-at-5-7">        <span class="cs-key">if</span> task.get("id") == expected:</span>
<span class="cs-ln cs-focus-at-8-1">            deleted = tasks.pop(index)</span>
<span class="cs-ln cs-focus-at-9-6">            save_tasks(tasks)</span>
<span class="cs-ln cs-focus-at-10-6">            <span class="cs-key">return</span> deleted</span>
<span class="cs-ln cs-focus-at-12-1">    <span class="cs-key">raise</span> ValueError(f"task {expected} was not found")</span></pre>
    </div>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">Two names tie the halves together</p>
  <div class="cs-split cs-split-code">
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/tools.py · lines 97–115</span></div>
      <pre class="cs-code-body cs-lines cs-from-97"><span class="cs-ln cs-focus-at-4-4">by_name = {</span>
<span class="cs-ln cs-focus-at-4-4">    "get_todays_date": get_todays_date,</span>
<span class="cs-ln cs-focus-at-4-4">    "create_task": create_task,</span>
<span class="cs-ln cs-focus-at-4-4">    "filter_tasks_by_text": filter_tasks_by_text,</span>
<span class="cs-ln cs-focus-at-4-4">    "filter_tasks_by_due_date": filter_tasks_by_due_date,</span>
<span class="cs-ln cs-focus-at-4-4">    "filter_tasks_by_status": filter_tasks_by_status,</span>
<span class="cs-ln cs-focus-at-4-4">    "update_task": update_task,</span>
<span class="cs-ln cs-focus-at-4-4">    "delete_task": delete_task,</span>
<span class="cs-ln cs-focus-at-4-4">}</span>
<span class="cs-ln"></span>
<span class="cs-ln cs-focus-at-10-3">definitions = [</span>
<span class="cs-ln cs-focus-at-10-3">    {</span>
<span class="cs-ln cs-focus-at-10-3">        "type": "function",</span>
<span class="cs-ln cs-focus-at-10-3">        "function": {</span>
<span class="cs-ln cs-focus-at-10-3">            "name": "get_todays_date",</span>
<span class="cs-ln cs-focus-at-10-3">            "description": "Return today's date as YYYY-MM-DD.",</span>
<span class="cs-ln cs-focus-at-10-3">            "parameters": {"type": "object", "properties": {}},</span>
<span class="cs-ln cs-focus-at-10-3">        },</span>
<span class="cs-ln cs-focus-at-10-3">    },</span></pre>
    </div>
    <div class="cs-stack">
      <div class="cs-card cs-at-4-4 cs-until-10-3"><p class="cs-card-label">by_name</p><p class="cs-card-title">Tool name → Python function. call_tool uses it.</p></div>
      <div class="cs-card cs-at-10-3 cs-until-17-1"><p class="cs-card-label">definitions</p><p class="cs-card-title">All 7 schemas, sent as tools</p></div>
      <div class="cs-card cs-card-accent cs-at-17-1"><p class="cs-card-label">Remember</p><p class="cs-card-title">The model sees definitions. Your program runs by_name.</p></div>
    </div>
  </div>
</div>

<div class="course-slide cs-center">
  <p class="cs-kicker">agent/bot.py</p>
  <p class="cs-pill">API call · store · tools</p>
  <h2 class="cs-title cs-at-9-8">The part that <span class="cs-hl">decides</span></h2>
  <p class="cs-pill cs-at-13-9"><span class="cs-hl">This is where tool calling happens</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">agent/bot.py · two limits</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/bot.py · lines 6–8</span></div>
    <pre class="cs-code-body cs-lines cs-from-6"><span class="cs-ln"><span class="cs-key">class</span> Bot:</span>
<span class="cs-ln cs-focus-at-0-9 cs-focus-at-2-9">    search_limit = 5</span>
<span class="cs-ln cs-focus-at-0-9 cs-focus-at-4-6">    response_limit = 8</span></pre>
  </div>
  <p class="cs-pill cs-at-6-3">What each one counts: in a moment</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Bot.__init__</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/bot.py · lines 10–19</span></div>
    <pre class="cs-code-body cs-lines cs-from-10"><span class="cs-ln cs-focus-at-0">    <span class="cs-key">def</span> __init__(self):</span>
<span class="cs-ln cs-focus-at-0">        self._llm = Llm()</span>
<span class="cs-ln cs-focus-at-2-6">        self._system_message = (</span>
<span class="cs-ln cs-focus-at-2-6 cs-focus-at-5-1">            "You are a task agent. Use the tools to read and change tasks. "</span>
<span class="cs-ln cs-focus-at-2-6 cs-focus-at-8-3">            "To find a task from the user's words, call filter_tasks_by_text "</span>
<span class="cs-ln cs-focus-at-2-6 cs-focus-at-8-3">            "with a regular expression. If the result is empty, try a different pattern. "</span>
<span class="cs-ln cs-focus-at-2-6 cs-focus-at-13-2">            f"Use at most {self.search_limit} searches, then ask the user to clarify. "</span>
<span class="cs-ln cs-focus-at-2-6">            "Reply briefly."</span>
<span class="cs-ln cs-focus-at-2-6">        )</span>
<span class="cs-ln cs-focus-at-14-9">        self._turns: list[dict] = []</span></pre>
  </div>
</div>

<div class="course-slide cs-center">
  <p class="cs-kicker">self._turns</p>
  <h2 class="cs-title cs-at-0-7">The memory of <span class="cs-hl">this chat</span></h2>
  <p class="cs-pill cs-at-4-4">Gone when the program stops</p>
  <p class="cs-pill cs-at-9-2"><span class="cs-hl">Real app: Redis, plus a snapshot in the database</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Bot.chat · once per user message</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/bot.py · lines 21–32</span></div>
    <pre class="cs-code-body cs-lines cs-from-21"><span class="cs-ln cs-focus-at-0">    <span class="cs-key">def</span> chat(self, user_message: str) -&gt; str:</span>
<span class="cs-ln">        """Reply to one user message, running any tool calls the model requests."""</span>
<span class="cs-ln cs-focus-at-3-9">        <span class="cs-key">if</span> not isinstance(user_message, str) or user_message.strip() == "":</span>
<span class="cs-ln cs-focus-at-3-9">            <span class="cs-key">raise</span> ValueError("user_message is empty")</span>
<span class="cs-ln"></span>
<span class="cs-ln cs-focus-at-6-1">        self._turns.append({"role": "user", "content": user_message})</span>
<span class="cs-ln cs-focus-at-8-5">        messages: list[dict] = [</span>
<span class="cs-ln cs-focus-at-8-5">            {"role": "system", "content": self._system_message},</span>
<span class="cs-ln cs-focus-at-8-5">            *self._turns,</span>
<span class="cs-ln cs-focus-at-8-5">        ]</span>
<span class="cs-ln cs-focus-at-20-6">        searches = 0</span>
<span class="cs-ln cs-focus-at-20-6">        allow_tools = True</span></pre>
  </div>
  <p class="cs-pill cs-at-13-7">The messages list from generate_response: system first, then the chat</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Bot.chat · the loop</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/bot.py · lines 34–38</span></div>
    <pre class="cs-code-body cs-lines cs-from-34"><span class="cs-ln cs-focus-at-0">        <span class="cs-key">for</span> _ in range(self.response_limit):</span>
<span class="cs-ln cs-focus-at-7-6">            message = self._llm.generate_response(</span>
<span class="cs-ln cs-focus-at-7-6">                messages,</span>
<span class="cs-ln cs-focus-at-10-6">                tools=definitions if allow_tools else None,</span>
<span class="cs-ln">            )</span></pre>
  </div>
  <div class="cs-row">
    <span class="cs-chip cs-at-3-9">At most 8 model requests per message</span>
    <span class="cs-chip cs-at-12-2">Tools only while allow_tools</span>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">Bot.chat · the way out</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/bot.py · lines 34–46</span></div>
    <pre class="cs-code-body cs-lines cs-from-34"><span class="cs-ln">        <span class="cs-key">for</span> _ in range(self.response_limit):</span>
<span class="cs-ln">            message = self._llm.generate_response(</span>
<span class="cs-ln">                messages,</span>
<span class="cs-ln">                tools=definitions if allow_tools else None,</span>
<span class="cs-ln">            )</span>
<span class="cs-ln cs-focus-at-0">            <span class="cs-key">if</span> not message.tool_calls:</span>
<span class="cs-ln cs-focus-at-5-8">                reply = message.content or ""</span>
<span class="cs-ln cs-focus-at-5-8">                <span class="cs-key">if</span> not reply:</span>
<span class="cs-ln cs-focus-at-5-8">                    <span class="cs-key">raise</span> ValueError("model returned an empty response")</span>
<span class="cs-ln cs-focus-at-8-5">                final = {"role": "assistant", "content": reply}</span>
<span class="cs-ln cs-focus-at-8-5">                messages.append(final)</span>
<span class="cs-ln cs-focus-at-8-5">                self._turns.append(final)</span>
<span class="cs-ln cs-focus-at-11-7">                <span class="cs-key">return</span> reply</span></pre>
  </div>
  <p class="cs-pill cs-at-15-9"><span class="cs-hl">No tool calls means the model is done</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Tool calls · store the request first</p>
  <div class="cs-split cs-split-code">
    <div class="cs-code">
      <div class="cs-code-bar"><span class="cs-code-path">agent/helpers.py · lines 71–85</span></div>
      <pre class="cs-code-body cs-lines cs-from-71"><span class="cs-ln cs-focus-at-5"><span class="cs-key">def</span> assistant_message(message) -&gt; dict:</span>
<span class="cs-ln cs-focus-at-5">    payload = {"role": "assistant", "content": message.content}</span>
<span class="cs-ln cs-focus-at-11-9">    <span class="cs-key">if</span> message.tool_calls:</span>
<span class="cs-ln cs-focus-at-11-9">        payload["tool_calls"] = [</span>
<span class="cs-ln cs-focus-at-11-9">            {</span>
<span class="cs-ln cs-focus-at-11-9 cs-focus-at-13 cs-focus-at-16-7">                "id": call.id,</span>
<span class="cs-ln cs-focus-at-11-9">                "type": "function",</span>
<span class="cs-ln cs-focus-at-11-9">                "function": {</span>
<span class="cs-ln cs-focus-at-11-9 cs-focus-at-13">                    "name": call.function.name,</span>
<span class="cs-ln cs-focus-at-11-9 cs-focus-at-13">                    "arguments": call.function.arguments,</span>
<span class="cs-ln cs-focus-at-11-9">                },</span>
<span class="cs-ln cs-focus-at-11-9">            }</span>
<span class="cs-ln cs-focus-at-11-9">            <span class="cs-key">for</span> call in message.tool_calls</span>
<span class="cs-ln cs-focus-at-11-9">        ]</span>
<span class="cs-ln">    <span class="cs-key">return</span> payload</span></pre>
    </div>
    <div class="cs-stack">
      <div class="cs-card cs-at-2-6 cs-until-9-8"><p class="cs-card-label">First</p><p class="cs-card-title">Store the model’s request</p></div>
      <div class="cs-card cs-at-9-8 cs-until-13"><p class="cs-card-label">Role</p><p class="cs-card-title">assistant</p></div>
      <div class="cs-card cs-at-13 cs-until-16-7"><p class="cs-card-label">Each call</p><p class="cs-card-title">Its id, function name, and arguments</p></div>
      <div class="cs-card cs-at-16-7 cs-until-20-6"><p class="cs-card-label">The id</p><p class="cs-card-title">Made by the API to name this one call</p></div>
      <div class="cs-card cs-card-accent cs-at-20-6"><p class="cs-card-label">Careful</p><p class="cs-card-title">Not a task id</p></div>
    </div>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">Tool calls · run each one</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/bot.py · lines 48–63</span></div>
    <pre class="cs-code-body cs-lines cs-from-48"><span class="cs-ln cs-focus-at-0">            assistant = assistant_message(message)</span>
<span class="cs-ln cs-focus-at-0">            messages.append(assistant)</span>
<span class="cs-ln cs-focus-at-0">            self._turns.append(assistant)</span>
<span class="cs-ln cs-focus-at-3-9">            <span class="cs-key">for</span> call in message.tool_calls:</span>
<span class="cs-ln cs-focus-at-19-4">                <span class="cs-key">if</span> call.function.name == "filter_tasks_by_text":</span>
<span class="cs-ln cs-focus-at-19-4">                    searches += 1</span>
<span class="cs-ln">                    <span class="cs-key">if</span> searches &gt; self.search_limit:</span>
<span class="cs-ln">                        allow_tools = False</span>
<span class="cs-ln">                        content = (</span>
<span class="cs-ln">                            f"Search limit of {self.search_limit} reached. "</span>
<span class="cs-ln">                            "Ask the user to clarify."</span>
<span class="cs-ln">                        )</span>
<span class="cs-ln">                    <span class="cs-key">else</span>:</span>
<span class="cs-ln">                        content = call_tool(call)</span>
<span class="cs-ln cs-focus-at-9-1">                <span class="cs-key">else</span>:</span>
<span class="cs-ln cs-focus-at-9-1">                    content = call_tool(call)</span></pre>
  </div>
  <p class="cs-pill cs-at-7">One reply can ask for several calls</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">The search limit</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/bot.py · lines 51–63</span></div>
    <pre class="cs-code-body cs-lines cs-from-51"><span class="cs-ln">            <span class="cs-key">for</span> call in message.tool_calls:</span>
<span class="cs-ln">                <span class="cs-key">if</span> call.function.name == "filter_tasks_by_text":</span>
<span class="cs-ln">                    searches += 1</span>
<span class="cs-ln cs-focus-at-0">                    <span class="cs-key">if</span> searches &gt; self.search_limit:</span>
<span class="cs-ln cs-focus-at-8">                        allow_tools = False</span>
<span class="cs-ln cs-focus-at-3-4">                        content = (</span>
<span class="cs-ln cs-focus-at-3-4">                            f"Search limit of {self.search_limit} reached. "</span>
<span class="cs-ln cs-focus-at-3-4">                            "Ask the user to clarify."</span>
<span class="cs-ln cs-focus-at-3-4">                        )</span>
<span class="cs-ln">                    <span class="cs-key">else</span>:</span>
<span class="cs-ln">                        content = call_tool(call)</span>
<span class="cs-ln">                <span class="cs-key">else</span>:</span>
<span class="cs-ln">                    content = call_tool(call)</span></pre>
  </div>
  <p class="cs-pill cs-at-10-1"><span class="cs-hl">From then on: no tools, so the model answers in words</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">The tool role, from llm.py</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/bot.py · lines 64–70</span></div>
    <pre class="cs-code-body cs-lines cs-from-64"><span class="cs-ln cs-focus-at-0-6">                tool_message = {</span>
<span class="cs-ln cs-focus-at-0-6 cs-focus-at-6-5">                    "role": "tool",</span>
<span class="cs-ln cs-focus-at-0-6 cs-focus-at-9-9">                    "tool_call_id": call.id,</span>
<span class="cs-ln cs-focus-at-0-6 cs-focus-at-8-1">                    "content": content,</span>
<span class="cs-ln cs-focus-at-0-6">                }</span>
<span class="cs-ln">                messages.append(tool_message)</span>
<span class="cs-ln">                self._turns.append(tool_message)</span></pre>
  </div>
  <p class="cs-pill cs-at-12-9"><span class="cs-hl">The call id pairs each result with its request</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Back to the top</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/bot.py · lines 34–72</span></div>
    <pre class="cs-code-body cs-lines cs-from-34"><span class="cs-ln cs-focus-at-4-3">        <span class="cs-key">for</span> _ in range(self.response_limit):</span>
<span class="cs-ln cs-gap">  # 29 lines</span>
<span class="cs-ln cs-from-64">                tool_message = {</span>
<span class="cs-ln">                    "role": "tool",</span>
<span class="cs-ln">                    "tool_call_id": call.id,</span>
<span class="cs-ln">                    "content": content,</span>
<span class="cs-ln">                }</span>
<span class="cs-ln cs-focus-at-0">                messages.append(tool_message)</span>
<span class="cs-ln cs-focus-at-0">                self._turns.append(tool_message)</span>
<span class="cs-ln"></span>
<span class="cs-ln cs-focus-at-8-7">        <span class="cs-key">raise</span> ValueError("tool calls did not finish")</span></pre>
  </div>
  <p class="cs-pill cs-at-16-6">The response limit: no endless loop</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">One turn</p>
  <h2 class="cs-title cs-at-0-6">One turn, <span class="cs-hl">six steps</span></h2>
  <ol class="cs-steps">
    <li class="cs-at-3-3">Append the user’s message</li>
    <li class="cs-at-5">Send the messages and the schemas</li>
    <li class="cs-at-7-2">Read the reply: text or tool calls</li>
    <li class="cs-at-9-9">Run each function in Python</li>
    <li class="cs-at-12">Send each result back with its call id</li>
    <li class="cs-at-14-5">Ask again, until there are no tool calls</li>
  </ol>
</div>

<div class="course-slide">
  <p class="cs-kicker">main.py · the test script</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">main.py · lines 1–16</span></div>
    <pre class="cs-code-body cs-lines cs-from-1"><span class="cs-ln"><span class="cs-key">from</span> agent.bot import Bot</span>
<span class="cs-ln"></span>
<span class="cs-ln cs-focus-at-5-1">bot = Bot()</span>
<span class="cs-ln cs-focus-at-5-1">print("Task agent. Type exit to stop.")</span>
<span class="cs-ln"></span>
<span class="cs-ln cs-focus-at-7-7"><span class="cs-key">while</span> True:</span>
<span class="cs-ln cs-focus-at-7-7">    <span class="cs-key">try</span>:</span>
<span class="cs-ln cs-focus-at-7-7">        user_message = input("You: ").strip()</span>
<span class="cs-ln">    <span class="cs-key">except</span> EOFError:</span>
<span class="cs-ln">        print()</span>
<span class="cs-ln">        break</span>
<span class="cs-ln cs-focus-at-10-5">    <span class="cs-key">if</span> user_message.lower() in {"exit", "quit"}:</span>
<span class="cs-ln cs-focus-at-10-5">        break</span>
<span class="cs-ln cs-focus-at-11-9">    <span class="cs-key">if</span> not user_message:</span>
<span class="cs-ln cs-focus-at-11-9">        continue</span>
<span class="cs-ln cs-focus-at-13-7">    print(f"Bot: {bot.chat(user_message)}")</span></pre>
  </div>
</div>

<div class="course-slide cs-center">
  <p class="cs-kicker">In a real product</p>
  <h2 class="cs-title cs-at-1-7">Terminal now, <span class="cs-hl">chat window</span> later</h2>
  <p class="cs-pill cs-at-6-1">Same chat method, same memory in turns</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">The test run</p>
  <h2 class="cs-title cs-at-3-8">Every message, saved in <span class="cs-mono">sample_chat.json</span></h2>
  <p class="cs-pill cs-at-0-9">Run from the three starting tasks</p>
  <p class="cs-pill cs-at-9-7"><span class="cs-hl">What the model asked for, and what came back</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">sample_chat.json · hello, then a list</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">sample_chat.json · lines 6–36</span></div>
    <pre class="cs-code-body cs-lines cs-from-6"><span class="cs-ln cs-focus-at-0">  {</span>
<span class="cs-ln cs-focus-at-0">    "role": "user",</span>
<span class="cs-ln cs-focus-at-0">    "content": "Hello, how are you?"</span>
<span class="cs-ln cs-focus-at-0">  },</span>
<span class="cs-ln cs-focus-at-0">  {</span>
<span class="cs-ln cs-focus-at-0">    "role": "assistant",</span>
<span class="cs-ln cs-focus-at-0">    "content": "Hello! I'm here to help you with your tasks. How can I assist you today?"</span>
<span class="cs-ln cs-focus-at-0">  },</span>
<span class="cs-ln cs-focus-at-4-5">  {</span>
<span class="cs-ln cs-focus-at-4-5">    "role": "user",</span>
<span class="cs-ln cs-focus-at-4-5">    "content": "I'd like to know what tasks do you see for me?"</span>
<span class="cs-ln cs-focus-at-4-5">  },</span>
<span class="cs-ln cs-focus-at-6-5">  {</span>
<span class="cs-ln cs-focus-at-6-5">    "role": "assistant",</span>
<span class="cs-ln cs-focus-at-6-5">    "content": null,</span>
<span class="cs-ln cs-focus-at-6-5">    "tool_calls": [</span>
<span class="cs-ln cs-focus-at-6-5">      {</span>
<span class="cs-ln cs-focus-at-6-5">        "id": "call_TuTL7UfpGkqPhXHfjjQWkkrF",</span>
<span class="cs-ln cs-focus-at-6-5">        "type": "function",</span>
<span class="cs-ln cs-focus-at-6-5">        "function": {</span>
<span class="cs-ln cs-focus-at-6-5 cs-focus-at-8-9">          "name": "filter_tasks_by_status",</span>
<span class="cs-ln cs-focus-at-6-5 cs-focus-at-8-9">          "arguments": "{\"status\":\"todo\"}"</span>
<span class="cs-ln cs-focus-at-6-5">        }</span>
<span class="cs-ln cs-focus-at-6-5">      }</span>
<span class="cs-ln cs-focus-at-6-5">    ]</span>
<span class="cs-ln cs-focus-at-6-5">  },</span>
<span class="cs-ln cs-focus-at-11-2">  {</span>
<span class="cs-ln cs-focus-at-11-2">    "role": "tool",</span>
<span class="cs-ln cs-focus-at-11-2">    "tool_call_id": "call_TuTL7UfpGkqPhXHfjjQWkkrF",</span>
<span class="cs-ln cs-focus-at-11-2 cs-focus-at-12-4">    "content": "[{\"id\": 1, \"title\": \"Buy groceries\", \"description\": \"Milk, eggs, bread, and coffee.\", \"status\": \"todo\", \"due_date\": \"2026-11-05\"}]"</span>
<span class="cs-ln cs-focus-at-11-2">  },</span></pre>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">sample_chat.json · two calls at once</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">sample_chat.json · lines 37–71</span></div>
    <pre class="cs-code-body cs-lines cs-from-37"><span class="cs-ln cs-focus-at-0">  {</span>
<span class="cs-ln cs-focus-at-0">    "role": "assistant",</span>
<span class="cs-ln cs-focus-at-0">    "content": null,</span>
<span class="cs-ln cs-focus-at-0">    "tool_calls": [</span>
<span class="cs-ln cs-focus-at-0">      {</span>
<span class="cs-ln cs-focus-at-0 cs-focus-at-4-9">        "id": "call_bFY7VOdx9bnOF2VDQdQ0EQdD",</span>
<span class="cs-ln cs-focus-at-0">        "type": "function",</span>
<span class="cs-ln cs-focus-at-0">        "function": {</span>
<span class="cs-ln cs-focus-at-0">          "name": "filter_tasks_by_status",</span>
<span class="cs-ln cs-focus-at-0 cs-focus-at-2-9">          "arguments": "{\"status\": \"in_progress\"}"</span>
<span class="cs-ln cs-focus-at-0">        }</span>
<span class="cs-ln cs-focus-at-0">      },</span>
<span class="cs-ln cs-focus-at-0">      {</span>
<span class="cs-ln cs-focus-at-0 cs-focus-at-4-9">        "id": "call_EF2kIRr9pNYJMPxYpmpmHkPD",</span>
<span class="cs-ln cs-focus-at-0">        "type": "function",</span>
<span class="cs-ln cs-focus-at-0">        "function": {</span>
<span class="cs-ln cs-focus-at-0">          "name": "filter_tasks_by_status",</span>
<span class="cs-ln cs-focus-at-0 cs-focus-at-2-9">          "arguments": "{\"status\": \"done\"}"</span>
<span class="cs-ln cs-focus-at-0">        }</span>
<span class="cs-ln cs-focus-at-0">      }</span>
<span class="cs-ln cs-focus-at-0">    ]</span>
<span class="cs-ln cs-focus-at-0">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln">    "role": "tool",</span>
<span class="cs-ln cs-focus-at-4-9">    "tool_call_id": "call_bFY7VOdx9bnOF2VDQdQ0EQdD",</span>
<span class="cs-ln">    "content": "[{\"id\": 2, \"title\": \"Write the tutorial outline\", \"description\": \"List the sections for the tool-calling lesson.\", \"status\": \"in_progress\", \"due_date\": \"2026-11-03\"}]"</span>
<span class="cs-ln">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln">    "role": "tool",</span>
<span class="cs-ln cs-focus-at-4-9">    "tool_call_id": "call_EF2kIRr9pNYJMPxYpmpmHkPD",</span>
<span class="cs-ln">    "content": "[{\"id\": 3, \"title\": \"Call the dentist\", \"description\": \"Schedule a cleaning for next month.\", \"status\": \"done\", \"due_date\": \"2026-10-28\"}]"</span>
<span class="cs-ln">  },</span>
<span class="cs-ln cs-focus-at-7-9">  {</span>
<span class="cs-ln cs-focus-at-7-9">    "role": "assistant",</span>
<span class="cs-ln cs-focus-at-7-9">    "content": "Here are your current tasks:\n\n**To Do:**\n1. Buy groceries - Milk, eggs, bread, and coffee. (Due: 2026-11-05)\n\n**In Progress:**\n1. Write the tutorial outline - List the sections for the tool-calling lesson. (Due: 2026-11-03)\n\n**Done:**\n1. Call the dentist - Schedule a cleaning for next month. (Completed on: 2026-10-28)\n\nLet me know if you need further assistance with any of these tasks!"</span></pre>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">sample_chat.json · the delete</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">sample_chat.json · lines 73–98</span></div>
    <pre class="cs-code-body cs-lines cs-from-73"><span class="cs-ln cs-focus-at-0-5">  {</span>
<span class="cs-ln cs-focus-at-0-5">    "role": "user",</span>
<span class="cs-ln cs-focus-at-0-5">    "content": "I don't like to buy milk anymore, are you able to remove that task for me?"</span>
<span class="cs-ln cs-focus-at-0-5">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln">    "role": "assistant",</span>
<span class="cs-ln">    "content": null,</span>
<span class="cs-ln">    "tool_calls": [</span>
<span class="cs-ln">      {</span>
<span class="cs-ln">        "id": "call_RZtuZmdaNkyLzz3tKId5xWna",</span>
<span class="cs-ln">        "type": "function",</span>
<span class="cs-ln">        "function": {</span>
<span class="cs-ln cs-focus-at-13-6">          "name": "delete_task",</span>
<span class="cs-ln cs-focus-at-13-6">          "arguments": "{\"task_id\":1}"</span>
<span class="cs-ln">        }</span>
<span class="cs-ln">      }</span>
<span class="cs-ln">    ]</span>
<span class="cs-ln">  },</span>
<span class="cs-ln cs-focus-at-16-7">  {</span>
<span class="cs-ln cs-focus-at-16-7">    "role": "tool",</span>
<span class="cs-ln cs-focus-at-16-7">    "tool_call_id": "call_RZtuZmdaNkyLzz3tKId5xWna",</span>
<span class="cs-ln cs-focus-at-16-7">    "content": "{\"id\": 1, \"title\": \"Buy groceries\", \"description\": \"Milk, eggs, bread, and coffee.\", \"status\": \"todo\", \"due_date\": \"2026-11-05\"}"</span>
<span class="cs-ln cs-focus-at-16-7">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln">    "role": "assistant",</span>
<span class="cs-ln">    "content": "The task to buy groceries has been removed. If there's anything else you need, feel free to let me know!"</span></pre>
  </div>
  <p class="cs-pill cs-at-5-4"><span class="cs-bad">No <span class="cs-mono">filter_tasks_by_text</span> call</span></p>
  <p class="cs-pill cs-at-9-5">It reused id 1, still in turns</p>
</div>

<div class="course-slide">
  <p class="cs-kicker">sample_chat.json · the gym task</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">sample_chat.json · lines 100–126</span></div>
    <pre class="cs-code-body cs-lines cs-from-100"><span class="cs-ln cs-focus-at-1-2">  {</span>
<span class="cs-ln cs-focus-at-1-2">    "role": "user",</span>
<span class="cs-ln cs-focus-at-1-2">    "content": "Can you add a new task, tomoorow I'd like to go to the gym with my friends, at 3 pm"</span>
<span class="cs-ln cs-focus-at-1-2">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln">    "role": "assistant",</span>
<span class="cs-ln">    "content": null,</span>
<span class="cs-ln">    "tool_calls": [</span>
<span class="cs-ln">      {</span>
<span class="cs-ln">        "id": "call_IOAGbjlB8Rabg6I2g4fvv86x",</span>
<span class="cs-ln">        "type": "function",</span>
<span class="cs-ln">        "function": {</span>
<span class="cs-ln cs-focus-at-6-8">          "name": "create_task",</span>
<span class="cs-ln cs-focus-at-6-8 cs-focus-at-9-2">          "arguments": "{\"title\":\"Go to the gym with friends\",\"description\":\"Go to the gym with friends at 3 PM.\",\"status\":\"todo\",\"due_date\":\"2023-11-01\"}"</span>
<span class="cs-ln">        }</span>
<span class="cs-ln">      }</span>
<span class="cs-ln">    ]</span>
<span class="cs-ln">  },</span>
<span class="cs-ln cs-focus-at-12-3">  {</span>
<span class="cs-ln cs-focus-at-12-3">    "role": "tool",</span>
<span class="cs-ln cs-focus-at-12-3">    "tool_call_id": "call_IOAGbjlB8Rabg6I2g4fvv86x",</span>
<span class="cs-ln cs-focus-at-12-3">    "content": "{\"id\": 4, \"title\": \"Go to the gym with friends\", \"description\": \"Go to the gym with friends at 3 PM.\", \"status\": \"todo\", \"due_date\": \"2023-11-01\"}"</span>
<span class="cs-ln cs-focus-at-12-3">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln cs-focus-at-18-5">    "role": "assistant",</span>
<span class="cs-ln cs-focus-at-18-5">    "content": "The task to go to the gym with your friends at 3 PM tomorrow has been added. If you have any more plans or need help, just let me know!"</span>
<span class="cs-ln">  },</span></pre>
  </div>
  <p class="cs-pill cs-at-4-6"><span class="cs-bad">No <span class="cs-mono">get_todays_date</span> call first</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">sample_chat.json · today’s date</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">sample_chat.json · lines 128–160</span></div>
    <pre class="cs-code-body cs-lines cs-from-128"><span class="cs-ln cs-focus-at-0">    "role": "user",</span>
<span class="cs-ln cs-focus-at-0">    "content": "what day is today?"</span>
<span class="cs-ln cs-focus-at-0">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln">    "role": "assistant",</span>
<span class="cs-ln">    "content": null,</span>
<span class="cs-ln">    "tool_calls": [</span>
<span class="cs-ln">      {</span>
<span class="cs-ln">        "id": "call_XrkAyOtVUp76qNRqoqzYDBiR",</span>
<span class="cs-ln">        "type": "function",</span>
<span class="cs-ln">        "function": {</span>
<span class="cs-ln cs-focus-at-3">          "name": "get_todays_date",</span>
<span class="cs-ln">          "arguments": "{}"</span>
<span class="cs-ln">        }</span>
<span class="cs-ln">      }</span>
<span class="cs-ln">    ]</span>
<span class="cs-ln">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln cs-focus-at-5-2">    "role": "tool",</span>
<span class="cs-ln cs-focus-at-5-2">    "tool_call_id": "call_XrkAyOtVUp76qNRqoqzYDBiR",</span>
<span class="cs-ln cs-focus-at-5-2">    "content": "\"2026-11-02\""</span>
<span class="cs-ln">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln">    "role": "assistant",</span>
<span class="cs-ln">    "content": "Today is November 2, 2026."</span>
<span class="cs-ln">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln cs-focus-at-8-6">    "role": "user",</span>
<span class="cs-ln cs-focus-at-8-6">    "content": "So then why did you add tomorrow as 1st of noember?"</span>
<span class="cs-ln">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln cs-focus-at-12-9">    "role": "assistant",</span>
<span class="cs-ln cs-focus-at-12-9">    "content": "I apologize for the oversight. I added the task with the wrong date. Would you like me to update the task to reflect the correct date, November 3, 2026?"</span></pre>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">sample_chat.json · the update</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">sample_chat.json · lines 162–188</span></div>
    <pre class="cs-code-body cs-lines cs-from-162"><span class="cs-ln">  {</span>
<span class="cs-ln cs-focus-at-0">    "role": "user",</span>
<span class="cs-ln cs-focus-at-0">    "content": "yes"</span>
<span class="cs-ln">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln">    "role": "assistant",</span>
<span class="cs-ln">    "content": null,</span>
<span class="cs-ln">    "tool_calls": [</span>
<span class="cs-ln">      {</span>
<span class="cs-ln">        "id": "call_873uFbutl4IXOUspLwvLu5iT",</span>
<span class="cs-ln">        "type": "function",</span>
<span class="cs-ln">        "function": {</span>
<span class="cs-ln cs-focus-at-1-1">          "name": "update_task",</span>
<span class="cs-ln cs-focus-at-1-1 cs-focus-at-3-5">          "arguments": "{\"task_id\":4,\"due_date\":\"2026-11-03\"}"</span>
<span class="cs-ln">        }</span>
<span class="cs-ln">      }</span>
<span class="cs-ln">    ]</span>
<span class="cs-ln">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln">    "role": "tool",</span>
<span class="cs-ln cs-focus-at-7-2">    "tool_call_id": "call_873uFbutl4IXOUspLwvLu5iT",</span>
<span class="cs-ln cs-focus-at-7-2">    "content": "{\"id\": 4, \"title\": \"Go to the gym with friends\", \"description\": \"Go to the gym with friends at 3 PM.\", \"status\": \"todo\", \"due_date\": \"2026-11-03\"}"</span>
<span class="cs-ln">  },</span>
<span class="cs-ln">  {</span>
<span class="cs-ln">    "role": "assistant",</span>
<span class="cs-ln">    "content": "The task has been updated to the correct date, November 3, 2026. Let me know if there's anything else you need!"</span>
<span class="cs-ln">  }</span></pre>
  </div>
</div>

<div class="course-slide">
  <p class="cs-kicker">After the chat</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">tasks.after.json · lines 1–23</span></div>
    <pre class="cs-code-body cs-lines cs-from-1 cs-focus-at-2-7"><span class="cs-ln">[</span>
<span class="cs-ln cs-focus-at-6-8">  {</span>
<span class="cs-ln cs-focus-at-6-8">    "id": 2,</span>
<span class="cs-ln cs-focus-at-6-8">    "title": "Write the tutorial outline",</span>
<span class="cs-ln cs-focus-at-6-8">    "description": "List the sections for the tool-calling lesson.",</span>
<span class="cs-ln cs-focus-at-6-8">    "status": "in_progress",</span>
<span class="cs-ln cs-focus-at-6-8">    "due_date": "2026-11-03"</span>
<span class="cs-ln cs-focus-at-6-8">  },</span>
<span class="cs-ln cs-focus-at-6-8">  {</span>
<span class="cs-ln cs-focus-at-6-8">    "id": 3,</span>
<span class="cs-ln cs-focus-at-6-8">    "title": "Call the dentist",</span>
<span class="cs-ln cs-focus-at-6-8">    "description": "Schedule a cleaning for next month.",</span>
<span class="cs-ln cs-focus-at-6-8">    "status": "done",</span>
<span class="cs-ln cs-focus-at-6-8">    "due_date": "2026-10-28"</span>
<span class="cs-ln cs-focus-at-6-8">  },</span>
<span class="cs-ln cs-focus-at-9-3">  {</span>
<span class="cs-ln cs-focus-at-9-3">    "id": 4,</span>
<span class="cs-ln cs-focus-at-9-3">    "title": "Go to the gym with friends",</span>
<span class="cs-ln cs-focus-at-9-3">    "description": "Go to the gym with friends at 3 PM.",</span>
<span class="cs-ln cs-focus-at-9-3">    "status": "todo",</span>
<span class="cs-ln cs-focus-at-9-3 cs-focus-at-11">    "due_date": "2026-11-03"</span>
<span class="cs-ln cs-focus-at-9-3">  }</span>
<span class="cs-ln">]</span></pre>
  </div>
  <p class="cs-pill cs-at-5-2"><span class="cs-bad">Task 1: gone</span></p>
  <p class="cs-pill cs-at-12-5">The program never reads this file. It is there to compare.</p>
</div>

<div class="course-slide cs-center">
  <p class="cs-kicker">The lesson</p>
  <p class="cs-pill cs-at-2-8 cs-until-9">The tool existed. It was not called.</p>
  <h2 class="cs-title cs-at-9">The model <span class="cs-hl">chooses</span>. Your code runs.</h2>
  <p class="cs-pill cs-at-15-4"><span class="cs-hl">A past-date check would have caught it</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Why it matters</p>
  <h2 class="cs-title">That split is <span class="cs-hl">the loop</span></h2>
  <p class="cs-pill cs-at-5-9">The skill behind those AI engineer job posts</p>
  <p class="cs-pill cs-at-9-1"><span class="cs-hl">An agent = this loop + more tools + better checks</span></p>
</div>

<div class="course-slide cs-center">
  <p class="cs-kicker">Leave with this</p>
  <ul class="cs-checks">
    <li class="cs-at-1-3">The model chooses the function</li>
    <li class="cs-at-3-4">Your code runs it</li>
    <li class="cs-at-4-7">The result is not the answer until you send it back and ask again</li>
  </ul>
</div>

<div class="course-slide">
  <p class="cs-kicker">Your turn</p>
  <div class="cs-grid cs-cols-2">
    <div class="cs-card cs-at-1-1"><p class="cs-card-label">Quiz · tip page</p><p class="cs-card-title">One step or function. Say what it does.</p></div>
    <div class="cs-card cs-at-11-4"><p class="cs-card-label">Practice</p><p class="cs-card-title">A <span class="cs-mono">create_task</span> call for tomorrow, with a made-up date</p></div>
  </div>
  <p class="cs-pill cs-at-6-5">YouTube: the description links to the tip page</p>
  <p class="cs-pill cs-at-16-8"><span class="cs-hl">What runs before it is saved? What goes back before asking again?</span></p>
</div>

<div class="course-slide cs-center">
  <p class="cs-kicker">The real challenge</p>
  <p class="cs-pill cs-at-4-6">Treat it like a product before it ships</p>
  <h2 class="cs-title cs-at-8-4">Find what <span class="cs-hl">breaks</span>. Fix it. Prove it.</h2>
  <p class="cs-pill cs-at-12-6"><span class="cs-hl">No answer file. Hints only.</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Bug 1 · the wrong year</p>
  <h2 class="cs-title cs-at-2">Why did tomorrow become <span class="cs-bad">2023</span>?</h2>
  <p class="cs-pill cs-at-5-4">Hint: no clock. When it skips <span class="cs-mono">get_todays_date</span>, it guesses.</p>
  <div class="cs-code">
    <div class="cs-code-bar"><span class="cs-code-path">agent/bot.py · lines 12–18</span></div>
    <pre class="cs-code-body cs-lines cs-from-12"><span class="cs-ln cs-focus-at-11-8">        self._system_message = (</span>
<span class="cs-ln cs-focus-at-11-8">            "You are a task agent. Use the tools to read and change tasks. "</span>
<span class="cs-ln cs-focus-at-11-8 cs-focus-at-15-2">            "To find a task from the user's words, call filter_tasks_by_text "</span>
<span class="cs-ln cs-focus-at-11-8 cs-focus-at-15-2">            "with a regular expression. If the result is empty, try a different pattern. "</span>
<span class="cs-ln cs-focus-at-11-8">            f"Use at most {self.search_limit} searches, then ask the user to clarify. "</span>
<span class="cs-ln cs-focus-at-11-8">            "Reply briefly."</span>
<span class="cs-ln cs-focus-at-11-8">        )</span></pre>
  </div>
  <p class="cs-pill cs-at-16-9"><span class="cs-bad">Nothing here about dates</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Bug 1 · hints, not answers</p>
  <ol class="cs-steps">
    <li class="cs-at-0-1">Your first fix may start in the <span class="cs-hl">prompt</span></li>
    <li class="cs-at-2-6">What could your <span class="cs-hl">code</span> check before a task is saved?</li>
    <li class="cs-at-8-7">Run the same chat again. Is the date right?</li>
  </ol>
</div>

<div class="course-slide">
  <p class="cs-kicker">Bug 2 · the delete</p>
  <div class="cs-code cs-no-copy">
    <div class="cs-code-bar"><span class="cs-code-path">sample_chat.json · lines 75, 86, 94</span></div>
    <pre class="cs-code-body cs-lines cs-from-75"><span class="cs-ln cs-focus-at-1-7">    "content": "I don't like to buy milk anymore, are you able to remove that task for me?"</span>
<span class="cs-ln cs-gap">  # 10 lines</span>
<span class="cs-ln cs-from-86">          "arguments": "{\"task_id\":1}"</span>
<span class="cs-ln cs-gap">  # 7 lines</span>
<span class="cs-ln cs-from-94 cs-focus-at-5-2">    "content": "{\"id\": 1, \"title\": \"Buy groceries\", \"description\": \"Milk, eggs, bread, and coffee.\", \"status\": \"todo\", \"due_date\": \"2026-11-05\"}"</span></pre>
  </div>
  <p class="cs-pill cs-at-8-7">Hint: decide the right behavior first</p>
  <div class="cs-row">
    <span class="cs-chip cs-at-11-7">The prompt?</span>
    <span class="cs-chip cs-at-12-6">The tools?</span>
    <span class="cs-chip cs-at-13-2">The code?</span>
  </div>
  <p class="cs-pill cs-at-15-4"><span class="cs-hl">Run that chat again to prove it</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Find new ways it breaks</p>
  <h2 class="cs-title cs-at-2-6">Write test chats like <span class="cs-hl">test cases</span></h2>
  <ul class="cs-checks">
    <li class="cs-at-6-5">A task that does not exist</li>
    <li class="cs-at-9-1">Two tasks with almost the same title</li>
    <li class="cs-at-13-6">“Next Friday”, “the end of the month”</li>
    <li class="cs-at-17-6">Three changes in one message</li>
    <li class="cs-at-20-3">Something that has nothing to do with tasks</li>
  </ul>
</div>

<div class="course-slide">
  <p class="cs-kicker">For each test chat</p>
  <ol class="cs-steps">
    <li class="cs-at-0-9">Write down what should happen</li>
    <li class="cs-at-2-5">Run it, and compare</li>
    <li class="cs-at-4-1">Wrong? Fix the prompt, the schema, or the code</li>
    <li class="cs-at-9-1">Keep that chat as a test, and rerun it after every change</li>
  </ol>
</div>

<div class="course-slide">
  <p class="cs-kicker">On your résumé</p>
  <h2 class="cs-title cs-at-2-2">Built it. <span class="cs-hl">Tested it. Fixed it.</span></h2>
  <div class="cs-card cs-at-6-4"><p class="cs-card-label">For example</p><p class="cs-quote">Wrote test conversations for an LLM agent, found and fixed a date bug and an unsafe delete in its tool calls, and kept every failing chat as a test.</p></div>
  <p class="cs-pill cs-at-17-6"><span class="cs-hl">The real work it takes to ship an agent</span></p>
</div>

<div class="course-slide">
  <p class="cs-kicker">Stuck? Reach out</p>
  <div class="cs-grid cs-cols-2">
    <div class="cs-code cs-at-2-8">
      <div class="cs-code-bar"><span class="cs-code-path">Email</span></div>
      <pre class="cs-code-body">mohammad@iswad.tech</pre>
    </div>
    <div class="cs-code cs-at-8-7">
      <div class="cs-code-bar"><span class="cs-code-path">Mentorship</span></div>
      <pre class="cs-code-body">https://tipsbymoh.tech/services/mentorship</pre>
    </div>
  </div>
  <p class="cs-pill cs-at-10-2 cs-until-13-4">Both are in the notes under the video</p>
  <p class="cs-pill cs-at-13-4"><span class="cs-hl">Catch you in the next tip</span></p>
</div>