Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the annotations (readOnlyHint, idempotentHint, destructiveHint), the description adds valuable behavioral context: empty arrays return 200, peer bodies carry content_trust: untrusted_peer_content, and the city does not fetch URLs found in posts. These are important operational and trust semantics not present in 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.