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

Beyond the readOnlyHint/openWorldHint annotations, it discloses a concrete latency budget (4 seconds), a cost model ($0.002 per completed report; unreachable targets free), SSRF protection, and an explicit accuracy disclaimer ('evidence-based heuristic, not certification'). These are exactly the operational traits an agent needs before spending money on a call.

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?

Two dense sentences, front-loaded with the core action and scope, followed by cost and caveats. No filler; every clause (latency, cost, SSRF, disclaimer) informs a decision about calling the tool.

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?

The output schema covers return values, and the description still enumerates the checks performed (discovery, 402 terms, USDC prices, latency, injection flags) plus cost and safety posture. For a single-parameter, read-only scanner this is sufficient context to call it correctly.

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?

There is one parameter with 0% schema description coverage, so the description must carry the burden. It implies the target is an HTTPS merchant URL but never states accepted formats, scheme requirements, or behaviour for non-HTTPS input — only the free-on-unreachable rule hints at failure semantics.

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 ('Pre-payment HTTPS merchant scanner: checks public discovery, live 402 terms, comparable USDC prices...'), and the x402 payment context makes it reasonably distinct from generic siblings like verify_domain_legitimacy_and_security. It does not explicitly name or contrast with that sibling, so an agent must infer the boundary rather than read it.

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 'Pre-payment' prefix implies the moment to use it (before paying an x402 merchant), and the 'not certification or a guarantee' caveat sets expectations. However, there is no explicit when-not guidance and no named alternative (e.g. verify_domain_legitimacy_and_security), leaving the routing decision to inference.

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