Check whether your MCP server actually answers on the HTTP+SSE transport — and whether that is still enough for the clients you care about.
Once the transport is right, the remaining problem is that nobody can see what your server does. MCP Showcase turns the same URL into a live playground with documentation for every tool.
Usually the path ending in /sse, though servers mount it in various places.
Streamable HTTP first, then SSE — and the result tells you which one actually answered.
Handshake, protocol version and the full tool list, plus the raw request log.
The original HTTP transport for MCP. The client opens a long-lived Server-Sent Events stream to receive server-to-client messages, and POSTs its own messages to a separate endpoint. Two endpoints, one direction each. It works, and it is awkward behind proxies and load balancers in exactly the ways you would expect.
Paste your endpoint above and this connects the way a real client does — streamable HTTP first, then SSE — and tells you which one actually answered.
This is the failure worth understanding, because it produces no error message. Current clients try streamable HTTP first, and not all of them fall back. A server that only speaks SSE is then simply not there as far as that client is concerned — it reports an empty server or nothing at all, rather than a transport failure. Nothing in your logs will look wrong, because nothing reached you.
If your server used to appear in a client and stopped after an update, this is the first thing to check.
If you control the server, yes. Streamable HTTP is one endpoint instead of two, reconnects cleanly, and is what the ecosystem has settled on. Support both while you have users on older clients, then drop SSE. If you do not control the server, this page at least tells you which transport you are dealing with before you start debugging your client.
Once a client can reach your server, the remaining problem is that nobody can tell what it does. A tool list is not a demonstration, and a prospect will not install a client to find out. MCP Showcase points at the same URL and produces a live playground with generated documentation for every tool, so evaluating your server takes a click.