Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the readOnly and idempotent annotations, the description reveals ranking behavior (citation/bill/docket first), lexical matching semantics, the result limit, output format, and the recommended follow-up fetch(id). This is rich behavioral context that substantially aids invocation.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.