Metrx MCP Server

Instructions

Implementation Reference

• src/tools/experiments.ts:167-212 (handler)

  The stop_experiment tool handler - takes experiment_id and optional promote_winner parameters, stops a running model routing experiment via POST to /experiments/{id}/stop endpoint

  server.registerTool(
    'stop_experiment',
    {
      title: 'Stop Experiment',
      description:
        'Stop a running model routing experiment. The experiment results are preserved. ' +
        'If the treatment model won, you can optionally promote it as the new default. ' +
        'Do NOT use for pausing experiments temporarily — stopping is permanent.',
      inputSchema: {
        experiment_id: z.string().uuid().describe('The experiment ID to stop'),
        promote_winner: z
          .boolean()
          .default(false)
          .describe('If the treatment model won, apply it as the new default model'),
      },
      annotations: {
        readOnlyHint: false,
        destructiveHint: false,
        idempotentHint: true,
        openWorldHint: false,
      },
    },
    async ({ experiment_id, promote_winner }) => {
      const result = await client.post<{ status: string; promoted: boolean }>(
        `/experiments/${experiment_id}/stop`,
        { promote_winner: promote_winner ?? false }
      );
  
      if (result.error) {
        return {
          content: [{ type: 'text', text: `Error stopping experiment: ${result.error}` }],
          isError: true,
        };
      }
  
      const d = result.data!;
      let text = `✅ Experiment stopped. Status: ${d.status}`;
      if (d.promoted) {
        text += '\n🔄 Treatment model has been promoted as the new default.';
      }
  
      return {
        content: [{ type: 'text', text }],
      };
    }
  );

• src/index.ts:74-103 (registration)

  The registration middleware that wraps server.registerTool to add the metrx_ prefix to all tool names and applies rate limiting

  // ── Rate limiting middleware + metrx_ namespace prefix ──
  // All tools are registered exclusively as metrx_{name}.
  // The metrx_ prefix namespaces our tools to avoid collisions when
  // multiple MCP servers are used together.
  const METRX_PREFIX = 'metrx_';
  const originalRegisterTool = server.registerTool.bind(server);
  (server as any).registerTool = function (
    name: string,
    config: any,
    handler: (...handlerArgs: any[]) => Promise<any>
  ) {
    const wrappedHandler = async (...handlerArgs: any[]) => {
      if (!rateLimiter.isAllowed(name)) {
        return {
          content: [
            {
              type: 'text' as const,
              text: `Rate limit exceeded for tool '${name}'. Maximum 60 requests per minute allowed.`,
            },
          ],
          isError: true,
        };
      }
      return handler(...handlerArgs);
    };
  
    // Register with metrx_ prefix (only — no deprecated aliases)
    const prefixedName = name.startsWith(METRX_PREFIX) ? name : `${METRX_PREFIX}${name}`;
    originalRegisterTool(prefixedName, config, wrappedHandler);
  };