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

It discloses a lot beyond the readOnly/openWorld/idempotent annotations: it does not sign transactions, it does not touch the endpoint's state, each call is charged so repeats are not free (which explains the non-idempotent hint), and the verdict format is 'review or pass with reasons'. Cost and the legal-disclaimer caveat are exactly the kind of context annotations cannot carry.

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 purpose is front-loaded and each clause carries real information, but the pricing boilerplate ('$0.01/call via x402 USDC or a card key (/credits), first 25 free; failed calls free') and the specific worker example URL are noise an agent does not need to select or call the tool. The single dense semicolon-chained sentence is also hard to scan.

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?

With no output schema, the description still conveys the return shape ('review or pass verdict with reasons'), the checks performed, and the free-of-side-effect guarantee. The parameter is fully documented. Only the exact verdict fields and what happens on an unreachable or non-402 endpoint are left to discover.

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 only one parameter and the schema already describes it fully at 100%: an absolute public https URL, including any query string. The description adds an example URL, but no extra syntax or constraint beyond what the schema says. Baseline 3 applies.

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+resource+scope: auditing an x402 seller's 402 terms, payTo addresses, domain and assets before an agent pays. That is far more specific than a generic 'check'. It never names the near-identical sibling x402_check, so what separates the two is not stated explicitly.

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?

Use is clearly labelled: 'Use before the first payment to an unfamiliar x402 seller.' It also says 'Never signs' and 'Screening aid, not legal advice', which sets limits on when the verdict is enough. No alternative tool is named, so there is no explicit 'use X instead when…' guidance.

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