Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It only says 'select all clips' without disclosing whether the existing selection is replaced or extended, whether it applies to the active sequence, or how track targets are handled. This operation mutates selection state, so such details are important.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.