Tool

The server exposes one tool, echo:

• Input: an object with a required string field, text.
• Result: the supplied text as both text content and structuredContent.
• Annotation: read-only; the handler has no side effects.

The server uses stdio and MCP protocol version 2026-07-28. It does not need an HTTP listener, model credentials, or a database.

Build and test

bazel build //mcp/server:echo_server
bazel test //mcp/server:echo_server_test

Use with the run_js gateway

The echo server is also the example downstream MCP for the run_js gateway. Configure its executable path as a stdio server and allow the echo tool:

{
  "servers": [
    {
      "alias": "echo",
      "transport": "stdio",
      "command": "/absolute/path/to/bazel-bin/mcp/server/echo_server",
      "args": [],
      "allowTools": ["echo"]
    }
  ]
}

With that configuration, JavaScript can call await echo.echo({text: "hello"}) through the gateway. The gateway's setup guide covers registration and execution.