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MCP Gateway

MCP Gateway is a lightweight Model Context Protocol gateway that exposes one small MCP entry point for multiple downstream MCP services.

Instead of flattening every downstream tool into the client at startup, the gateway exposes a fixed discovery and routing API. Agents can list services, inspect tools for one service, fetch one schema, and then forward the actual tool call.

Features

• One MCP entry point for multiple downstream MCP services.

• Token-efficient discovery through a small fixed gateway tool surface.

• Stdio and Streamable HTTP downstream transports.

• Optional inbound Streamable HTTP endpoint enabled by CLI flags.

• Hot reload for service-pool config changes.

• Stops removed, disabled, or replaced downstream services during reload.

• Restarts failed downstream processes up to three times before marking them unavailable.

• Atomic config reload that keeps the previous valid config when a new config is invalid.

• Optional newline-delimited JSON file logging that never writes operational logs to MCP stdout.

• Version reporting through --version or -v.

Related MCP server: MCP Gateway (Parent MCP Server)

Why Use It

• Keep agent-side MCP configuration small: every agent connects to the gateway, while downstream services are managed in one config file.

• Reduce initial tool context: agents discover only the service, tool, and schema needed for the current task.

• Keep service lifecycle control centralized instead of duplicating command paths, environment variables, and secrets across multiple clients.

Quick Start

Install globally:

npm install -g @jadchene/mcp-gateway-service

Create a local config:

cp config.example.json config.json

Start the stdio gateway:

mcp-gateway-service --config ./config.json

Start with inbound Streamable HTTP:

mcp-gateway-service --config ./config.json --http --host 127.0.0.1 --port 3100 --path /mcp

Use stateless JSON responses for HTTP clients that expect direct JSON-RPC responses from POST:

mcp-gateway-service --config ./config.json --http --port 3100 --path /mcp --json-response

Check the installed version:

mcp-gateway-service --version
mcp-gateway-service -v

Configuration

Pass the config file by CLI argument:

mcp-gateway-service --config ./config.json

Or by environment variable:

MCP_GATEWAY_CONFIG=./config.json mcp-gateway-service

If neither is provided, the service tries config.json in the current working directory.

Config example:

{
  "logging": {
    "enable": false,
    "path": "./logs/mcp-gateway.log"
  },
  "services": [
    {
      "serviceId": "demo-echo",
      "enable": true,
      "name": "Demo Echo Service",
      "description": "Sample echo MCP service.",
      "transport": {
        "type": "stdio",
        "command": "node",
        "args": [
          "--experimental-strip-types",
          "examples/echo-service.ts"
        ]
      }
    },
    {
      "serviceId": "remote-http",
      "enable": false,
      "name": "Remote Streamable HTTP Service",
      "description": "Example downstream MCP service over Streamable HTTP.",
      "transport": {
        "type": "http",
        "url": "http://127.0.0.1:3200/mcp",
        "headers": {
          "Authorization": "Bearer ${MCP_TOKEN}"
        },
        "enableJsonResponse": false
      }
    }
  ]
}

Configuration notes:

• logging.enable defaults to false.

• logging.path is required only when logging.enable is true.

• Relative logging.path values are resolved from the config file directory.

• Service enable defaults to true; setting it to false skips that service.

• cwd and env are optional for stdio services.

• Stdio transport.framing may be line or content-length. When omitted, the gateway tries line and then content-length.

• HTTP downstream services use transport.type: "http" and transport.url.

• HTTP transport.headers provides static request headers.

• HTTP transport.enableJsonResponse enables stateless JSON response mode for that downstream service.

Inbound Streamable HTTP

Inbound HTTP is enabled only with --http. Passing --host, --port, --path, or --json-response without --http does not start an HTTP listener.

The HTTP endpoint uses the same path for GET and POST:

• GET /mcp opens the SSE read channel and returns the session in the Mcp-Session-Id response header.

• POST /mcp sends JSON-RPC messages. New clients should bind the session through the Mcp-Session-Id request header.

• Query-string sessionId is accepted for compatibility.

• The endpoint SSE event advertises the single path, such as /mcp.

Gateway Tools

The gateway exposes six public tools:

Default token-efficient workflow:

1. Call gateway_list_services once.

2. Call gateway_list_tools(serviceId) only when a service is needed. Use a toolName array for name keywords and a desc array for description keywords.

3. When all filtered matches need schemas, pass includeSchema: true; when exact tool names are already known, call gateway_get_tool_schema with a non-empty name array.

4. Call gateway_call_tool to execute the downstream tool.

5. Use gateway_get_service only for diagnostics.

6. Use gateway_manage_service only to reconnect, enable, or disable a service.

gateway_get_tool_schema.toolName is a required unique non-empty string array and returns a schemas object keyed by each requested exact tool name. Use a one-element array when requesting one schema.

gateway_list_tools.toolName and gateway_list_tools.desc are optional unique non-empty string arrays. Matching is case-insensitive and uses literal substrings. When both are present, a tool is returned when either its name or description matches any supplied keyword. Description matching can also hit negative guidance such as "when not to use", so inspect the returned descriptions before selecting a tool.

All gateway tools with stable structured content expose an outputSchema. gateway_call_tool intentionally omits a fixed output schema because it forwards arbitrary downstream results. Its arguments object is always required; pass {} for a downstream tool with no arguments.

gateway_manage_service actions:

• reconnect: retry the current downstream lifecycle without modifying config.

• enable: persist enable: true for the service and reload config.

• disable: persist enable: false for the service and reload config.

Skill Integration

This repository includes a public gateway skill:

• Skill path: skills/mcp-gateway/SKILL.md

Use it when your agent supports skills. It keeps discovery token-efficient and routes downstream calls through the minimal gateway contract.

MCP Client Configuration

Codex:

[mcp_servers.gateway]
command = "mcp-gateway-service"
args = ["--config", "./config.json"]

Gemini CLI:

{
  "mcpServers": {
    "gateway": {
      "type": "stdio",
      "command": "mcp-gateway-service",
      "args": ["--config", "./config.json"]
    }
  }
}

Claude Code:

{
  "mcpServers": {
    "gateway": {
      "type": "stdio",
      "command": "mcp-gateway-service",
      "args": ["--config", "./config.json"]
    }
  }
}

Streamable HTTP mode:

Start one shared HTTP gateway process first:

mcp-gateway-service --config ./config.json --http --host 127.0.0.1 --port 3100 --path /mcp

Then point MCP clients at the HTTP endpoint.

Codex:

[mcp_servers.gateway]
url = "http://127.0.0.1:3100/mcp"

Gemini CLI:

{
  "mcpServers": {
    "gateway": {
      "httpUrl": "http://127.0.0.1:3100/mcp"
    }
  }
}

Claude Code:

{
  "mcpServers": {
    "gateway": {
      "type": "http",
      "url": "http://127.0.0.1:3100/mcp"
    }
  }
}

Use the same URL for every client that should share the gateway service pool. Use --json-response only when your HTTP client expects stateless JSON-RPC responses directly from POST requests.

Development

npm install
npm run dev

Build and test:

npm run build
npm test

Run the built server:

node dist/index.js --config ./config.json

License

MIT. See LICENSE.