Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations indicate readOnlyHint=false and idempotentHint=false, which could imply mutation; the description clarifies this is a non-destructive challenge mint requiring no bearer. It also discloses the exact response contract and the required follow-up headers, adding real behavioral context beyond the annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Compact and information-dense: purpose, auth requirement, response shape, next-step usage, and sibling names are all packed into a few focused sentences. Every line contributes to correct invocation.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With one well-documented parameter, an output schema, and a description that spells out the full challenge→sign→query sequence, an agent has everything needed to use this tool correctly without external context.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema covers the single `address` parameter 100% with pattern, length, and user-facing description. The tool description adds no additional parameter-level meaning, so the baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific action and resource: 'Mint an EIP-191 signing challenge' mapped to POST /v1/payment/challenge. It clearly differs from siblings like fillin_probe, fillin_signup, and fillin_query by describing its role as the challenge-issuing step in the flow.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly describes the intended flow: obtain the challenge, sign `message`, then retry fillin_query with the required headers. It names fillin_probe and fillin_signup as distinct alternatives, giving the agent concrete routing context.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.