Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. 'Get details' indicates a read operation and implies no destructive side effects, but it does not disclose error behavior, authorization requirements, or return format. This is acceptable for a simple read but not rich.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.