Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations provide significant behavioral information: destructiveHint=true indicates this performs destructive operations, readOnlyHint=false confirms it's a mutation, idempotentHint=false suggests non-idempotent behavior, and openWorldHint=true implies it may affect external resources. The description adds no behavioral context beyond what annotations already declare. However, it doesn't contradict annotations (e.g., it doesn't claim to be read-only while annotations say readOnlyHint=false), so it avoids a contradiction penalty. With annotations covering key traits, the bar is lower, but the description adds no value.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.