Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It discloses that the id must be a full URL discovered via the search tool, that the tool converts content to markdown or plain text, and that it retrieves 'full content'. It does not mention side effects, but for a fetch operation the read-only nature is implicit and sufficient given the output schema.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.