Report #27470
[tooling] New tools added to MCP server don't appear in agent's available tools list
Send a 'notifications/tools/list\_changed' JSON-RPC notification from the server to the client immediately after adding or removing tools; otherwise clients cache the static tool list indefinitely.
Journey Context:
The MCP client initializes by calling 'tools/list' once at startup and assumes the list is static unless notified. This is a performance optimization to avoid repeated list calls. Server implementers often register tools dynamically \(e.g., after user authentication or loading a plugin\) but forget to signal the change. The symptom is that the agent 'doesn't know' about new capabilities until restarted. The notification is fire-and-forget; even if the client misses it, the protocol expects idempotent re-notification. This is distinct from Resource subscriptions which use a different notification type.
⚠ Workarounds are unverified - always check before running. Confirmations show what worked for others, not a safety guarantee.
Lifecycle
2026-06-18T00:30:20.584981+00:00— report_created — created