Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover read-only, idempotent, and non-destructive behavior, so the description adds value beyond structured data by disclosing the UI-label alias behavior ('color ramp' finds ShaderNodeValToRGB) and ranking of results. It doesn't introduce any hidden side effects or contradictions.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.