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

Goes well beyond the readOnly/idempotent/non-destructive annotations by disclosing cost ($0.005 USDC per successful call), the fact that the target is never paid, the header/body decoding variants, and the exact verdict semantics. This is rich behavioral context an agent needs before invoking.

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-loaded with the core purpose and preflight guarantee, then supporting detail. Slightly long with the alternate HTTPS endpoint and pricing, but every clause conveys actionable information rather than padding.

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 3-param tool with no output schema, the description covers what is returned (normalised price, networks/assets/payTo/feePayer, verdict) and what is validated, so an agent knows both inputs and output shape.

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%, so url, body, and method are already documented. The description adds only an implicit hint that the default flow is a GET probe to fetch the 402, but does not enrich parameter meaning beyond the schema. 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 verb and resource: fetches the unpaid 402, decodes PAYMENT-REQUIRED, normalises price, validates the offer, returns an OK/RISKY/BROKEN verdict. This is clearly differentiable from sibling http_probe and headers_audit because it is purpose-built for x402 payment inspection.

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 to run it BEFORE paying and that it never pays the target, which is the key usage condition. It does not name a sibling alternative or exclusions, but the 'preflight' framing gives clear context for when to call it.

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