Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the full burden. It discloses that the tool retrieves a list, implying a read-only operation without side effects. For a parameterless getter, this is sufficient; however, it does not specify the exact format of the returned list (e.g., file extensions vs MIME types).
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.