When adding new tools to the MCP toolbelt, TWO places must be updated: 1. **Rails Controller** (`/rails/app/controllers/api/v1/mcp_controller.rb`): - Add tool definition to `MCP_TOOLS` constant (name, description, parameters, handler) - Add handler method `handle_<tool_name>` with the implementation 2. **MCP Bridge** (`/rails/mcp-bridge/src/tools/index.ts`): - Add tool object to the `tools` array with: - `name`: tool name (snake_case) - `description`: what the tool does - `inputSchema`: JSON Schema for parameters - `execute`: async function calling `api.post('/mcp/execute', { tool: '...', params: args })` - After editing, rebuild: `npm run build` in `/rails/mcp-bridge` CRITICAL: Both places must be updated for the tool to be available to agents. Forgetting the TypeScript bridge is a common error.