Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint and destructiveHint, so safety is covered. The description adds meaningful behavioral context by disclosing that the returned definition body is from the current version, choosing 'published if any, else latest' — a non-obvious selection rule an agent needs to know.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.