Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations lack behavioral info (readOnlyHint=false, etc.), but description adds: returns proposal with terms, deliverables, checkout hand-off types, and 403 error for comparison-shopping. Side effects and authorization are not fully disclosed, but it's sufficient.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.