Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations declare the safety profile (not read-only, not idempotent, not destructive), and the description adds two useful facts beyond them: it is slow, and it returns added/updated counts. That latency and return-shape context is genuinely helpful since there is no output schema. It omits auth/permission requirements, keeping it short of a 5.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.