OpenAPI MCP Server (Hono + Node.js)

This project exposes an MCP server over HTTP using Hono at /mcp.

It gives three tools:

• api_search: find operations from an OpenAPI spec
• api_execute: call one operation by operationId (or method + path)
• session: store and read session variables (token, ids, etc.)

Requirements

• Node.js 18+ installed

Install

npm install

Run

npm run dev

Server endpoints:

• http://localhost:3000/
• http://localhost:3000/health
• http://localhost:3000/mcp

Configure environment (optional)

• OPENAPI_SPEC_URL: OpenAPI JSON URL (default: https://ag.nischal-dahal.com.np/api-docs-json)
• OPENAPI_SERVER_FILE_CACHE=1: optional, enable server-side file cache (disabled by default)
• API_BASE_URL: override API base URL used for execution
• PORT: HTTP server port (default 3000)

If the spec URL is temporarily unavailable (for example 502), the MCP server stays alive and returns a structured tool error with recovery hints instead of crashing.

Set OpenAPI URL via request headers (recommended)

You can provide spec configuration without session storage:

• ?url= query param on MCP endpoint (recommended for static MCP config)
• url header on MCP request
• authorization: optional auth header used when fetching the spec URL

Example:

POST /mcp?url=api.example.com/openapi.json
authorization: Bearer YOUR_TOKEN

Use with an MCP client

Add an MCP server entry that points to this URL:

{
  "mcpServers": {
    "openapi-hono": {
      "url": "https://dx.lexicon.website/mcp?url=https://ag.nischal-dahal.com.np/api-docs-json"
    }
  }
}

Where to set the OpenAPI spec URL

You can set the spec URL in three ways:

1. MCP URL query (recommended): configure .../mcp?url=... in your MCP client.

https://your-domain/mcp?url=https://your-api.com/openapi.json

1. Per request override: pass url in api_search or api_execute arguments.

{
  "name": "api_search",
  "arguments": {
    "query": "users list",
    "url": "api.example.com/openapi.json"
  }
}

Typical usage flow

1. Find operations:

{
  "name": "api_search",
  "arguments": {
    "query": "login auth token",
    "limit": 10
  }
}

1. Execute operation:

{
  "name": "api_execute",
  "arguments": {
    "operationId": "auth_login",
    "body": {
      "email": "[email protected]",
      "password": "secret"
    },
    "extractVariables": {
      "token": "$.data.token"
    }
  }
}

1. Reuse stored session token automatically (or inspect with session tool):

{
  "name": "session",
  "arguments": {
    "action": "getVariables"
  }
}

Note: only auth/token data is stored in session; OpenAPI URL is not read from session anymore.