Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, but the description adds a useful specific behavioral guarantee: it does not modify the working tree. This goes beyond the generic read-only hint and gives the agent confidence about side effects. It does not detail what information is returned or whether any operations are cached, but for a simple read-only tool this is adequate.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.