Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so the safety profile is covered. The description adds meaningful context beyond that: it reiterates the no-side-effect nature ('without sending a message') and pre-enumerates what is returned, so the agent knows this is a static informational lookup. Return format specifics are left to the output schema.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.