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

Annotations already carry readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds valuable context beyond that: the $0.02/call cost, the charging condition ('only charged when a result actually comes back'), and that the result is a 'dated crawl snapshot' implying data may be stale. No contradiction with annotations — readOnlyHint is consistent with a pre-payment vetting operation.

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?

The description is dense but every sentence earns its place: cost, purpose, signals, two-step workflow, and charging behavior. The most critical info (PAID, vet BEFORE paying) is front-loaded. It's longer than average but packed with necessary operational detail for a paid two-call workflow.

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?

For a paid two-step workflow with no output schema, the description covers the key operational aspects: the call sequence, the return value (A–F grade and the `accepts` array), and cost behavior. It doesn't detail error cases or the exact return structure of the grade result, but given there's no output schema, the essentials are addressed.

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 coverage is 100% with both parameters documented, so the baseline is 3. The description adds meaningful workflow context explaining how the two parameters interact: the first call omits x402_payment to get the `accepts` array, then the second call includes it as a base64 X-PAYLOAD payload. This explains parameter semantics beyond the schema.

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?

The description uses a specific verb+resource combination ('Vet an x402 seller') and a concrete output (A–F grade from observable signals: 402-spec fidelity, price sanity, payTo presence, TLS, latency). It clearly distinguishes this tool from its siblings, which are swap/predict/scan tools, by focusing on risk assessment of x402 providers before payment.

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?

The description gives explicit workflow guidance: call once WITHOUT x402_payment to receive requirements, pay, then call again with the payment payload. It also states when to use it ('BEFORE paying'). It doesn't explicitly name alternatives or when-not-to-use exclusions, but the workflow and context are clear enough to route an agent.

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