Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description's obligation is lighter. It adds the diagnostics performed, but says nothing about output shape, scoring scale, or length limits on the messages array beyond what the annotations and output schema already convey.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.