Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations cover idempotency and safety (idempotentHint=true, destructiveHint=false). The description adds crucial behavioral context that this sets implicit state affecting subsequent operations, which is essential for an agent to understand side effects. No contradiction with annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.