Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations provide readOnlyHint=true, and the description adds useful behavioral context: it verifies credentials, shows privileges, and returns a { data:{...} } shape. This goes beyond the annotation by describing the response format and the API endpoint. It does not mention error handling, but for a read-only auth check this is sufficient.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.