Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare the operation read-only, idempotent, and non-destructive. The description adds transparency by enumerating the exact data returned (bid/ask, last trade price, 24h volume, change percentage), which is useful beyond the annotations. No additional behavioral traits like rate limits or error handling are mentioned, but the annotations cover the safety profile.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.