Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, but the description adds genuinely useful context: synchronous execution, no auth required, and the semantic distinction between current-basket YTD returns and realized track record. It stops short of rate limits or response-size behavior, keeping it just below the top tier.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.