Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already convey non-read-only and non-destructive behavior. The description adds meaningful context: the HTTP endpoint (POST /create-space), the exact response fields, that it is a free call, and how the returned space_id should be used downstream. This goes beyond what annotations provide.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.