Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the burden. 'Get page information' implies a read-only operation, but lacks disclosure on error behavior, permissions, or whether the page must exist. The presence of an output schema partially alleviates the need to describe return values.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.