Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the full burden. It does disclose the core behavior and output formats, including the 'display-referred' PNG detail, which adds beyond the tool name. However, it does not mention where files are saved, whether the operation is synchronous or asynchronous, or whether it overwrites existing files.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.