Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare read-only, idempotent, non-destructive behavior, so the description is not burdened with safety disclosure. It adds meaningful behavioral context by disclosing that the default horizon is 7 days, 14 days requires SnowSure Pro, and My Mountains resorts work when signed in. It does not cover error behavior or rate limits, keeping it from a 5.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.