Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish the safety profile (readOnlyHint=true, destructiveHint=false), so the description only needs to add context. It does: it defines the derivation of the value (total minus burned) and clarifies the narrow output shape. It stops short of stating freshness/caching or numeric precision, which would be the remaining useful detail for a live supply metric.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.