Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the behavioral burden; it discloses the JSON return shape and filename auto-generation. It does not state whether an existing file is overwritten, whether charts are persisted to disk as a side effect, or what error behavior occurs for non-numeric columns, though filename and chart_path imply file output.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.