Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description contributes one genuinely useful trait beyond them — that results are heuristic and superseded by provider analyzers — but says nothing about handling of malformed input, partial coverage, or confidence levels.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.