Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It usefully discloses read-only access ('Read access to the design') and the ordering guarantee ('newest first'), plus per-field semantics for merged/archived branches, but says nothing about pagination, result limits, or what happens with large branch sets.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.