Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations at all, the description carries the full burden, and it does disclose the key behavioral facts: a mutation that creates a NEW layer (non-destructive to existing content) and that file order maps to frame order. It says nothing about frame-size compatibility, failure handling for missing paths, what happens if the document lacks an animation timeline, or what is returned.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.