Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare read-only, idempotent, and non-destructive behavior. The description adds the exchange source (Bitfinex), the live nature, and the special 'ALL' option—context beyond the annotations. It also lists returned fields (bid/ask, last, daily change, volume), which is useful even with an output schema present.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.