Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, and the description adds meaningful behavioral context: the test is grounded in the requirement sentence and clause, cites spec/section/page, and the generator abstains rather than inventing tests. This goes beyond annotations though it does not detail failure modes or return values, which are covered by the output schema.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.