Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds real behavioral context beyond that: longer periods return far more data and are 'trimmed harder', which warns the agent about result truncation. It still says nothing about auth or rate limits, but the trimming datum is genuine added value.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.