Fastify support or custom HTTP adapter?

[Njuelle]

Hi team,

I’m wondering how to use the MCP TypeScript SDK with a backend (NestJS) that uses Fastify instead of Express?

Currently, the SDK seems to be tightly coupled with Express, but it could be a great feature to support Fastify or provide a way to use a custom HTTP adapter so users can integrate their own.
What do you think would be the best approach?

I’d be happy to work on a PR for this :)

Thanks in advance!

[haroldadmin]

Hi, I maintain a plugin to run MCP servers over Fastify. I'm working on adding support for Streamable HTTP support, and it should be out soon it's out now!

https://github.com/haroldadmin/fastify-mcp

[eddyv]

Hm, i never had issues running mcp servers on fastify - anything in particular you had issues setting up? You can check out our impl here https://github.com/confluentinc/mcp-confluent/blob/c0927bc9def221105edff74b8f1a8fd36af2e092/src/mcp/transports/http.ts. Hopefully, this helps :)

[sjoerdvanBommel]

I've noticed several hooks such as onSend hook are skipped on tool call. I think this has to do with the fact that request.raw is used behind the scenes. See this blog post. Has anyone encountered the same, who was able to resolve this?

[sjoerdvanBommel]

Since we're skipping all the Fastify logic of handling the HTTP response when using request.raw, it will not execute further fastify hooks such as onSend.

I'm surprised though that the intialize and notifications/initialized methods behave different. In those cases, the hooks still get called. EDIT: initialize and notifications/initialized do not behave different. It looked like they did, because the onSend hook gets called. However, this is because during initialization, the GET endpoint is being called as well because of session management, which does not skip fastify HTTP response handling.

[KKonstantinov]

v2 will make it easier for many frameworks to integrate with - using web standards. follow #809 for it.