Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries full burden for behavioral disclosure. 'Mark a task as completed' implies a write/mutation operation but doesn't specify whether this requires special permissions, if the action is reversible, what happens to dependent items, or what confirmation/response to expect. For a mutation tool with zero annotation coverage, this is insufficient behavioral context.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.