Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already mark the tool read-only, idempotent, and non-destructive. The description adds meaningful behavior beyond that: no auth prerequisite, case-insensitive capability matching, network preference, and that the response contains a matched subset. No contradiction with annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.