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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds material context beyond them: the $0.003 USDC per-call cost charged only on success, the single-GET no-payment guarantee, the go/caution/no_go verdict vocabulary, and what a caller without a wallet receives. That is precisely the pricing, side-effect, and output-shape information an agent cannot infer from annotations.

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 framing question and the no-payment/cost guarantees are front-loaded, and the checklist is compressed into one dense clause. The enumeration of checks is long but every item is a distinct signal an agent would want before paying; only slight tightening is possible.

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?

There is no output schema, and the description compensates by naming the verdict values, the recommended payment option, and the findings it returns. Combined with the cost model and the no-wallet fallback, an agent has everything needed to decide whether and how to call it.

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%, so the baseline is 3; the description earns one more by tying max_usd to a concrete outcome ("amount vs your budget", above budget = no_go) and by framing url as the endpoint about to be paid. It adds relationship semantics rather than merely restating field descriptions.

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?

Opens with a specific question the tool answers ("Is this x402 endpoint safe to pay?") and then enumerates exactly what it inspects (payTo checksum, OFAC, canonical USDC, budget, price cross-checks against OpenAPI/x402scan, HTTPS, RDAP domain age). The resource and operation are unambiguous, and no sibling (about, list_rules, scan_text, scan_tools) overlaps with 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?

Usage is clearly implied and reinforced: call it before paying an x402 endpoint, and it explicitly states "never pays" and only sends one GET. It also covers the fallback case ("Without an x402 wallet you get the payment terms and the paid HTTP URL instead"). It does not name a sibling alternative, but the siblings are unrelated utilities, so no routing ambiguity exists.

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