Michael Brenndoerfer | Data & AI, Private Equity, Technology

Michael Brenndoerfer

Example: Adding a Calculator to Our Agent › Understanding the Tool Use Flow

Michael BrenndoerferJune 29, 20252 min read

AI Agent HandbookAll chapters

Part 5 of 15Tool Use - Extending the Agent's Abilities

Chapter 14Example: Adding a Calculator to Our Agent › Understanding the Tool Use Flow

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Section 9 of 16 · 2 min read

Example: Adding a Calculator to Our Agent › Understanding the Tool Use FlowOne section · Sections in this chapter9 / 16 ↓

Sections in this chapter16

Let's trace through exactly what happens when you ask "What's $1,234 \times 5,678$ ?":

Step 1: User Input

User: What's 1234 times 5678?

Step 2: Agent Analyzes the Question

Claude receives:

The user's message
The calculator tool description
Instructions to use tools when appropriate

Claude thinks: "This is a multiplication problem with large numbers. I should use the calculate tool to get the exact answer."

Step 3: Agent Requests Tool Use

Claude returns a response indicating it wants to use a tool:

In[11]:

Code

{
    "stop_reason": "tool_use",
    "content": [
        {
            "type": "tool_use",
            "name": "calculate",
            "input": {"expression": "1234 * 5678"}
        }
    ]
}

Out[11]:

Console

{'stop_reason': 'tool_use',
 'content': [{'type': 'tool_use',
   'name': 'calculate',
   'input': {'expression': '1234 * 5678'}}]}

Step 4: We Call the Tool

Our code extracts the tool name and input, then calls:

In[12]:

Code

calculate(expression="1234 * 5678")

Out[12]:

Console

{'success': True, 'result': 7006652, 'expression': '1234 * 5678'}

Which returns:

In[13]:

Code

{'success': True, 'result': 7006652, 'expression': '1234 * 5678'}

Out[13]:

Console

{'success': True, 'result': 7006652, 'expression': '1234 * 5678'}

Step 5: We Send the Result Back

We add the tool result to the conversation and send it back to Claude:

In[8]:

Code

messages.append({
    "role": "user",
    "content": [{
        "type": "tool_result",
        "tool_use_id": "...",
        "content": "{'success': True, 'result': 7006652, 'expression': '1234 * 5678'}"
    }]
})

Step 6: Agent Formulates Final Response

Claude receives the tool result and generates a natural response:

1,234 times 5,678 equals 7,006,652.

This entire flow happens in milliseconds. From the user's perspective, they just asked a question and got an accurate answer.