Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already carry readOnlyHint, idempotentHint, and destructiveHint, so the bar is lower. The description still adds meaningful context: the pledge row becomes WITHDRAWN rather than erased, the pledged total decreases, no money is refunded, the operation is free, and the same signature-gated authentication as pledging applies. It also clarifies the two-step flow with a time limit, which readOnlyHint alone wouldn't convey.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.