Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the readOnlyHint annotation, the description discloses important semantics: the stage buckets are exclusive, raised is the sum of the buckets, and it clarifies the meanings of committed/signed/wired. This is valuable behavioral insight not available from annotations alone.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.