Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden of behavioral disclosure. It only says 'URL-encode or URL-decode a string' without detailing the encoding scheme, special character handling, or any side effects, making it insufficient for informed invocation.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.