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

With no annotations, the description carries the full transparency burden and it delivers: it discloses that the request is live and unpaid, the method behavior ('GET only, except...'), public-host restriction with redirect re-checking, delisted-host never-contact, 60s caching, and rate limits. This is comprehensive behavioral disclosure beyond the schema.

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?

Three well-structured sentences front-load the core purpose and outputs, then add method nuances and operational constraints. Every clause carries necessary operational information, with no filler or redundancy.

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 two-parameter tool with an output schema, the description covers input semantics, behavioral constraints, rate limits, and the report contents. Since an output schema exists, the description need not detail the return structure. No essential information is missing for correct invocation.

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 0%, so the description must compensate. It adds meaning to 'url' as a 'public http(s) URL' and to 'method' with 'GET only, except that a URL already in the index is probed with its listed method' plus the default GET. It could be more explicit about allowed method values, but it substantially enriches the bare 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?

States a specific action ('Make ONE live unpaid request to a public http(s) URL') and concrete outputs ('status code, latency, alive flag, whether a PAYMENT-REQUIRED challenge came back and the parsed USD price'). This clearly differentiates it from sibling tools like x402_search or x402_service by focusing on probing a single URL for endpoint status.

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?

Provides clear context on when to use the tool: to probe a URL and determine if it is an x402 endpoint. It also gives operational constraints (GET method, public hosts only, delisted hosts never contacted, cache and rate limits). However it does not explicitly name alternative tools or state when not to use this tool versus siblings like x402_search.

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