When configuring Claude Desktop to connect to a remote (non-localhost) MCP server, the connection requires HTTPS. Using a plain http:// URL will not produce a clear protocol error; instead, the local bridge process will start, send the initialize JSON-RPC message, and then crash with: Server transport closed unexpectedly.

Diagnosis

To isolate this failure from general server errors, replicate the JSON-RPC initialize handshake directly via curl over HTTP (with correct Content-Type/Accept headers). If the HTTP curl request succeeds cleanly but Claude Desktop fails with the transport error, the issue is Claude's HTTPS requirement.

Resolution

Deploy a TLS-terminating reverse proxy (such as Caddy or Nginx with Let's Encrypt certificates) in front of the remote MCP server endpoint to expose it over HTTPS.