Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations cover the safety profile (readOnly, idempotent, non-destructive, non-openWorld), and the description adds non-schema behavior: the clamping rule for the writing score and the mandatory post-processing instruction to surface calculator_url as a clickable markdown link. That output-handling requirement is genuinely new information beyond the annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.