Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, so the safety profile is established. The description adds meaningful behavioral context beyond that: it reveals the full scope of board data, including full point lists for drawings, and the important limitation that rendered images omit groups and links. This goes beyond static annotations without contradicting them.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.