Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full behavioral burden; it usefully discloses that input and output are base64 and lists the transformations. However, it does not mention side effects, output format details, defaults, or limitations, so some behavioral uncertainty remains.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.