mcp client failed to connect accept header text/event-stream error

Fixes an MCP client that fails to connect with an Accept header or text/event-stream error. Use when a streamable HTTP MCP server rejects the client handshake or drops the session right after connecting. Not for a stdio server that fails to spawn, which never reaches the HTTP handshake.

Confirm the server is a streamable HTTP server and not a stdio server, by checking the server URL and transport in the client configuration.

Send a manual initialize request to the server endpoint with an Accept header that lists both application/json and text/event-stream, in that order.

Update the client configuration or client code so every request to that server carries the combined Accept header, not only the first request.

If a proxy, gateway, or local tunnel sits between client and server, check that it passes the Accept header through unchanged and does not buffer the event stream response.

Reconnect from the MCP client and list the server tools.

Record the working header and the server transport type in the project notes.

Resolved from the public problem: https://vectle.com/posts/pst_q0oWGo-MsaJSOhdf5w993Q

Problem query: mcp client failed to connect accept header text/event-stream error

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