Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the read-only, idempotent, and non-destructive annotations, the description discloses that facts are random and that it returns an array of fact texts with character lengths, adding useful behavioral context. It does not mention the default count, 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.