Enable Function Calling in Mistral Agents Using Standard JSON Schema

 This updated tutorial guides developers through enabling function calling in Mistral Agents via the standard JSON Schema format Function calling allows agents to invoke external APIs or tools (like weather or flight data services) dynamically during conversation—extending their reasoning capabilities beyond text generation.

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🧩 Why Function Calling?

• Seamless tool orchestration: Enables agents to perform actions—like checking bank interest rates or flight statuses—in real time.

• Schema-driven clarity: JSON Schema ensures function inputs and outputs are well-defined and type-safe.

• Leverage MCP Orchestration: Integrates with Mistral's Model Context Protocol for complex workflows 

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🛠️ Step-by-Step Implementation

1. Define Your Function

Create a simple API wrapper, e.g.:

python
def get_european_central_bank_interest_rate(date: str) -> dict:
    # Mock implementation returning a fixed rate
    return {"date": date, "interest_rate": "2.5%"}

2. Craft the JSON Schema

Define the function parameters so the agent knows how to call it:

python
tool_def = {
  "type": "function",
  "function": {
    "name": "get_european_central_bank_interest_rate",
    "description": "Retrieve ECB interest rate",
    "parameters": {
      "type": "object",
      "properties": { "date": {"type": "string"} },
      "required": ["date"]
    }
  }
}

3. Create the Agent

Register the agent with Mistral's SDK:

python
agent = client.beta.agents.create(
  model="mistral-medium-2505",
  name="ecb-interest-rate-agent",
  description="Fetch ECB interest rate",
  tools=[tool_def],
)

The agent now recognizes the function and can decide when to invoke it during a conversation.

4. Start Conversation & Execute

Interact with the agent using a prompt like, "What's today's interest rate?"

• The agent emits a function.call event with arguments.

• You execute the function and return a function.result back to the agent.

• The agent continues based on the result.

This demo uses a mocked example, but any external API can be plugged in—flight info, weather, or tooling endpoints 

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✅ Takeaways

• JSON Schema simplifies defining callable tools.

• Agents can autonomously decide if, when, and how to call your functions.

• This pattern enhances Mistral Agents’ real-time capabilities across knowledge retrieval, action automation, and dynamic orchestration.