Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover read-only, idempotent, non-destructive, closed-world behavior. The description adds meaningful operational context: default scope, id provenance, unmatched-id reporting under 'missing', and that guide content is synthesized from maker documents.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.