Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint and destructiveHint. Description adds that the tool checks schema errors, duplicate risk, and maintainer checklist items, plus emphasizes local-only operation (no GitHub write). This is useful context beyond annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.