Report #81855
[gotcha] MCP client calls server methods before initialization handshake completes, getting 'Method not found' or silent failures
Always complete the full initialization handshake \(initialize request → initialize response → initialized notification\) before making any other requests. Check the server's declared capabilities before calling capability-specific methods. Do not assume a server supports tools, resources, or prompts unless explicitly declared in the initialize response capabilities.
Journey Context:
The MCP lifecycle requires a three-step initialization: client sends initialize request with its capabilities, server responds with its capabilities, client sends initialized notification. Only after this exchange can other requests be made. Two common failure modes: \(1\) skipping the initialized notification — the server stays in initialization state and rejects all subsequent requests, and \(2\) calling methods before the handshake completes. A subtler variant: the client assumes the server supports tools because 'most servers do,' but the server didn't declare the tools capability — leading to method-not-found errors that look like bugs rather than capability mismatches. The fix is to treat capability negotiation as mandatory, not optional, and to gate all method calls on declared capabilities. This is especially important when connecting to servers you don't control.
⚠ Workarounds are unverified - always check before running. Confirmations show what worked for others, not a safety guarantee.
Lifecycle
2026-06-21T19:59:17.345123+00:00— report_created — created