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openapi-mcp

Transports

Compare the stdio, web (SSE), streamable-http and cloudflare-worker transports and pick the right one for your MCP server.

By Updated

Choose a transport with --transport (or -t). The default is stdio.

Generated servers speak MCP 2026-07-28 (stateless requests, server/discover) and keep serving 2025-era clients that open with initialize, using the MCP TypeScript SDK v2. The web (SSE) transport stays on the 2025-era protocol because the specification deprecates HTTP+SSE; prefer streamable-http for new deployments.

stdio#

Communicates with MCP clients over standard input and output. Ideal for local development and desktop clients that launch the server as a process. The server picks the protocol era from each connection's opening message.

bash
openapi-mcp-generator -i ./openapi.json -o ./my-mcp
cd my-mcp && npm install && npm start

web (SSE)#

Launches an HTTP server built with Hono that uses Server-Sent Events for server-to-client messages and a REST endpoint for client-to-server messages. Supports multiple connections and serves the browser playground at /.

bash
openapi-mcp-generator -i ./openapi.json -o ./my-mcp --transport=web --port=3000
cd my-mcp && npm install && npm run start:web

streamable-http#

Implements the MCP Streamable HTTP transport, also built with Hono:

  • Stateless JSON-RPC over HTTP: every request gets a fresh server, so it scales behind any load balancer.
  • Serves MCP 2026-07-28 and 2025-era clients. 2025-era clients run without sessions, and GET and DELETE on the endpoint answer 405.
  • Proper HTTP status codes, and the browser playground at /.
bash
openapi-mcp-generator -i ./openapi.json -o ./my-mcp --transport=streamable-http --port=3000
cd my-mcp && npm install && npm run start:http

cloudflare-worker#

Generates a complete Cloudflare Workers project that serves the MCP server over Streamable HTTP at /mcp, using createMcpHandler from @modelcontextprotocol/server.

  • Stateless, and runs on the free Workers tier with no Durable Objects or KV. A fresh MCP server is created per request.
  • Lean dependencies: @modelcontextprotocol/server and @cfworker/json-schema.
  • Uses the global fetch, and validates arguments against the JSON Schema with no code generation and no eval.
  • Answers CORS on /mcp, so browser-based MCP clients such as the hosted playground can reach it. Access is still controlled by the Authorization header.
  • Serves the browser playground at /.

See Deploy to Cloudflare Workers.

Comparison#

Feature stdio web (SSE) streamable-http cloudflare-worker
Protocol JSON-RPC over stdio JSON-RPC over SSE JSON-RPC over HTTP Streamable HTTP at /mcp
Connection Persistent Persistent Request/response Request/response
Multiple clients No Yes Yes Yes
Browser compatible No Yes Yes Yes
Firewall friendly No Yes Yes Yes
Load balancing No Limited Yes Yes (edge)
Status codes No Limited Full HTTP codes Full HTTP codes
Browser playground No Yes Yes Yes
Hosting Local Self-hosted Self-hosted Cloudflare (serverless)

Browser playground#

Servers generated for web, streamable-http and cloudflare-worker serve a playground at / (http://localhost:<port>/, or http://localhost:8787/ with npm run dev for a Worker). It lists the tools, builds a form for each one from its input schema, runs it and shows every JSON-RPC message. See Connect clients.

To stop serving it, for example in production:

  • Node servers (web, streamable-http): set MCP_PLAYGROUND=off in the environment or .env.
  • Workers: set the MCP_PLAYGROUND var to "off" in wrangler.jsonc under vars.
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