Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and non-destructive behavior, so the description does not need to repeat those. The description adds the response size constraint (<2 KB) and hints at temporal coverage through 'historical state mutations,' but does not describe caching, rate limits, or data freshness beyond what the parameter schema already covers.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.