Tool Registry & Dispatch

The problem, from first principles

Between the model's tool call and the actual function sits a registry: a table that knows which tools exist, describes them to the model, and dispatches calls by name. This is the core idea of protocols such as the Model Context Protocol (MCP), where a server lists its tools and a client calls them by name with arguments. The dispatcher must be defensive. An unknown tool name is a normal event (models hallucinate), and a tool that raises an exception must not crash the agent. Both should come back as a structured error result the model can read and react to.

From theory to code

Implement the class ToolRegistry.

Constraints

• register(name, fn, description) stores the tool. Registering an existing name raises ValueError.
• list_tools() returns a list of {'name': ..., 'description': ...} dicts sorted by name.
• call(name, args) returns {'ok': True, 'result': fn(**args)} on success.
• If name is not registered return {'ok': False, 'error': 'unknown tool: {name}'}. If the tool raises an exception e, return {'ok': False, 'error': 'tool error: {e}'} (using str(e)). Never let an exception escape call.

Hints