Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations provide no safety hints beyond destructiveHint=false, so the description carries the burden. It adds a key behavioral trait: if estimated_impact_usd is not provided, a default is calculated from severity. This goes beyond the schema and is valuable for understanding tool behavior.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.