Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover read-only, idempotent, non-destructive, so the bar is lower. The description still adds real value beyond them: newest-first ordering, 'metadata only' return scope, and the sp500+ tier requirement with sample data rejected — a genuine access constraint the agent cannot infer from structured fields. It does not state default page size behavior in prose, but the schema covers that.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.