Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered. The description adds real value beyond them by disclosing output semantics (reading time at 200 wpm, speaking time at 130 wpm) and the post-call obligation to surface calculator_url as a markdown link.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.