Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries full responsibility for behavioral disclosure. It only states what the tool does, not whether it's read-only, how results are ordered, whether search is case-sensitive, or any limits. The existence of an output schema covers return structure, but not behavioral traits like pagination or performance.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.