Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the readOnlyHint, the description discloses the output structure (images + citation index), the billing model (flat /query rate, free rendering), and a behavioral caveat (vision models paraphrase), which is useful context. It does not contradict annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.