Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations cover safety profile (readOnly=false, destructive=false, idempotent=false). Description adds valuable context the annotations cannot: no automatic reply, confirm exact wording before sending, send only user's own words. Doesn't disclose what happens on error or rate limits, but for a feedback submission the write semantics are well-covered.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.