Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With readOnlyHint=true, the safety profile is already clear. The description adds the return behavior ('Returns a JSON object'), which is valuable because there is no output schema. It does not disclose error handling or invalid-input behavior, but for a straightforward conversion tool this is sufficient.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.