Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description adds substantial behavioral context beyond readOnlyHint=true: it explains the EIP-191 signing identity, binding to lexicon version, bundle hash and card hash, the per-tool canonical-name and x-vocab checks, the unmapped-argument listing, refusal before charge for agents without schemas, the per-call price, and that API keys do not cover this tool. These are exactly the operational, billing, and precondition details an agent needs beyond annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.