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

There are no annotations, so the description carries the full burden. It discloses that the tool is paid, costs $0.01 USDC via x402, and that calling without payment returns payment instructions. It also states it performs a live probe and returns PASS/CAUTION/AVOID with evidence. While it doesn't detail every side effect (e.g., network requests to the target) or auth, it transparently surfaces the key cost and payment behavior.

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 clause earns its place: it lists specific audit components, states the return type, and communicates cost/payment fallback. It is not as minimal as possible but remains focused and readable without fluff.

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?

Given one parameter, no output schema, and no annotations, the description reasonably explains what happens (audit checks), what comes back (PASS/CAUTION/AVOID with evidence), and the payment flow. It doesn't cover timing or failure modes, but for a single-URL audit tool, the core context is present.

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?

The input schema already covers the only parameter fully: 'Absolute https URL of the x402 resource to audit' is a clear description. The tool description adds context that the URL is a merchant's endpoint, but no additional param semantics beyond the schema. This matches the baseline for high schema coverage.

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 clearly names the tool's action ('Full paid due-diligence audit' of an x402 merchant) and enumerates specific checks: live probe, price-drift detection, settlement history, unique buyer count, and on-chain verification. This differentiates it from sibling x402_check_endpoint by emphasizing a comprehensive audit rather than a basic endpoint check.

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 implies when to use the tool — when a thorough, paid audit is needed — and warns that it costs $0.01 USDC, suggesting it is a heavier operation than simpler alternatives. However, it does not explicitly name alternatives or state when NOT to use it, leaving the choice between this and x402_check_endpoint to inference.

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