Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover read-only, idempotent, non-destructive behavior. The description adds value by disclosing conditional outcomes: `authenticated:true` with empty `pending[]` versus returning `connect_url` when credentials are missing. This goes beyond the annotation hints without contradicting them.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.