I recently wrote an MCP server, in node, after trying and failing to get the official javascript SDK to work. I agree with the criticisms — this is a stunningly bad specification, perhaps the worst I have seen in my career. I don’t think the authors have actually tried to use it.

Trying to fix “you must hold a single connection open to receive all responses and notifications” by replacing it with “you must hold open as many connections as you have long-running requests, plus one more for notifications” is downright unhinged, and from reading the spec I’m not even sure they know that’s what they are asking clients to do