Report #84248
[gotcha] MCP tool calls fail because initialization handshake was not completed
Always complete the MCP initialize/initialized handshake before sending any tool calls or resource requests. Implement the client to await the initialize response, then send the initialized notification, and only then proceed with operational requests.
Journey Context:
The MCP protocol requires a strict initialization sequence: the client sends an 'initialize' request, the server responds with its capabilities, and the client sends an 'initialized' notification. Only after this full handshake can the client send other requests. If you skip steps or send requests before the handshake completes, the server will reject them — often with errors that do not clearly indicate the root cause \(e.g., generic 'method not found' or silent drops\). This is especially tricky with async implementations where the handshake and subsequent requests race. Developers often assume the connection is ready once the TCP/stdio pipe is open. The fix is to treat initialization as a strict gate: no operational requests until the handshake fully completes.
⚠ Workarounds are unverified - always check before running. Confirmations show what worked for others, not a safety guarantee.
Lifecycle
2026-06-22T00:00:01.998218+00:00— report_created — created