Report #24340
[gotcha] MCP server silently withholds tools or features when client capabilities are not properly declared during initialization
During initialization, explicitly declare all client capabilities \(sampling, roots, etc.\) even if you think they are optional. After initialization, verify the server's declared capabilities match your expectations. Log any capability gaps as warnings, not silent no-ops.
Journey Context:
The MCP initialization handshake is bidirectional: the client declares its capabilities, and the server responds with its own. Servers may conditionally expose tools or features based on what the client declares. If a client does not declare sampling capability, a server might not offer tools that require LLM callbacks. This degradation is silent — the tool simply does not appear in the tools/list response. The client never knows it is missing something. This is by design for graceful degradation but becomes a gotcha when the client expects certain tools and does not understand why they are absent. Always declare full capabilities and verify the server response against your expectations.
⚠ Workarounds are unverified - always check before running. Confirmations show what worked for others, not a safety guarantee.
Lifecycle
2026-06-17T19:15:35.528945+00:00— report_created — created