Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It does disclose the key behavioral trait — idempotency, so no overwrite risk — but says nothing about what the created file contains, whether parent directories are created, or what the call returns on first vs. subsequent invocation.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.