who: price and coverage (free)

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

Annotations cover only readOnlyHint and openWorldHint; the description adds the material economics the annotation cannot: no payment, no wallet required, the concrete price ($0.05 USDC on Base mainnet), and the free-refusal behavior on bad input. It stops short of describing pagination, caching or rate limits, so a 4 rather than a 5.

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?

Front-loads the key fact ('FREE, read-only') and then explains purpose, usage, and the edge case in four tight sentences. Slightly dense with parentheticals, but every sentence carries information an agent needs.

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?

There is no output schema, but the description enumerates the returned fields (price, asset, network, payee, coverage statement) and explains the failure response, so the agent knows both the success and failure shapes. Complete for a single-parameter, read-only tool.

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 description coverage is 100% and the `q` parameter already documents the accepted forms (name, domain, LEI, jurisdiction suffix). The description references 'the subject' generically but adds no syntax or format detail beyond the schema, so the baseline 3 applies.

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 verb and resource ('Returns the advertised x402 payment terms for a `who` lookup') and enumerates the returned fields — price, asset, network, payee, coverage statement. It is immediately distinguishable from its sibling `who`, which performs the actual paid lookup.

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 tells the agent when to call it: 'Use this before `who` to decide whether the lookup is worth the money.' It also covers the negative case — malformed, missing or ambiguous subjects return a free refusal rather than terms — so the agent knows what a non-term response means.

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