Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and non-destructive behavior. The description adds a useful behavioral nuance: 'open_only is ignored when status is set' (in schema) and the description mentions both filters without detailing precedence, but the schema covers it. The description itself adds the 'for an agent' scope, which is not in annotations. It contributes a small but meaningful behavioral detail beyond the annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.