Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
readOnlyHint=true already tells the agent this is a safe read, so the bar is lower. The description adds that the payload covers both supported networks and their RPC capabilities, which is useful signal about content, but says nothing about auth requirements, result size, caching, or ordering.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.