Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The annotations already declare the tool as read-only, idempotent, and non-destructive. The description adds useful behavioral context by clarifying that validation covers syntax and common typos, which implies a local, deterministic check rather than a deliverability or mailbox-existence check.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.