The other day I was toying with the MCP server (https://github.com/modelcontextprotocol/typescript-sdk). I default to bun these days and the http based server simply did not register in claude or any other client. No error logs, nothing.

After fiddling with my code I simply tried node and it just worked.

Now if you convert the request / response types to native bun server, it can be finicky.

But it works fine using express under bun with the official protocol implementation for typescript.

Actually writing a book about this too and will be using bun for it https://leanpub.com/creatingmcpserverswithoauth