Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden, and it does disclose the 30s cap and the default screenshot return. However it omits what happens on timeout (error, partial capture, or silent return) and whether waiting beyond 30s is clamped or rejected.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.