Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full behavioral burden, and it does disclose the one genuinely useful trait: readOnly=true suppresses modifications. It is silent on side effects an agent needs — whether opening replaces the currently active drawing, what happens if the file is missing or already open, and whether the bridge must be running.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.