Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false), so the description earns credit for the extra disclosures it does make: the a= tag is a bare URL so VMC vs CMC cannot be determined, and the DMARC p=quarantine/reject precondition that mail clients enforce. It does not discuss caching behavior or the force_refresh default, which remains with the schema.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.