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

With no annotations, the description carries the transparency burden. It discloses that the call is free, keyless, and neutral, and it enumerates the response fields including the recommended_action verdict and evidence components. It stops short of describing error cases or failure behavior, but it is materially transparent.

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 compact and front-loaded, with the core action in the first clause. Every sentence contributes either usage timing or output details, with no filler.

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?

Even without an output schema, the description enumerates the full expected return set and the call context, which is enough for an agent to invoke and interpret the result. It leaves out edge-case behavior (e.g., invalid target format), but the single parameter and clear phase make it largely complete.

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 sole parameter 'target' has 100% schema description coverage, so the description need not repeat it. It does restate 'resource URL or a 0x payTo address' but adds no syntax, format, or constraint detail beyond the 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?

The description opens with a specific verb and resource: 'Check an x402 payee BEFORE paying it', and lists concrete return values (recommended_action, flags, taint, etc.). This clearly separates it from x402_leaderboard/x402_profile and other security-lookup siblings.

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?

It explicitly instructs when to use the tool: 'Call this in your onBeforeSettle / pre-payment step' and says it never decides for you, implying an advisory role. It does not name alternative tools or exclusions, but the placement guidance is unambiguous.

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