Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already mark it read-only, idempotent, and non-destructive. The description adds useful behavioral context by disclosing the dataset domain and that the response includes caveats and per-tool examples; the output schema handles return shape, so omission of return format is minor.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.