Bridge an MCP Server or Custom Tool

Tool vs command: who calls whom

A command is triggered by the user through the UI. A tool is called by the model itself when it decides a function would help. If you want the agent to act on its own, you register a tool.

Path A — register a custom tool

ctx.tools.register({
  name: 'read_local_file',
  description: 'Read a text file from the workspace',
  parameters: {
    type: 'object',
    properties: { path: { type: 'string' } },
    required: ['path'],
  },
  async execute(args) {
    return { ok: true, content: await fs.readFile(args.path, 'utf8') };
  },
});

Three details matter: a clear description (it steers model selection), a strict JSON Schema for parameters, and structured error returns.