How to Define and Call a Tool in an AI Agent

Give your agent the ability to act: define a tool with a schema, and dispatch it when the model calls it.

Steps

1. Write the tool schema: name, a clear description, and a strict input JSON schema.
2. Register the tool in the tools list you pass to the API.
3. Write a dispatcher function that maps the tool name to real code and runs it.
4. In the loop, when stop_reason is tool_use, extract each tool_use block's name and input.
5. Run the dispatcher for each and collect the results.
6. Append the results as a tool_result message keyed to each tool_use_id, then loop.
7. Keep the description and schema precise — that's what the model actually reads.