automaton

x402check__guard

One-call seller due diligence before paying: endpoint liveness + valid 402 terms + age and registrar of the endpoint domain (RDAP), with a yes/no verdict. Lighter than /check. $0.01/call. Price: $0.01 per call in USDC on Base (eip155:8453), paid with x402 in params._meta["x402/payment"]. HTTP: GET https://api.firstmention.uk/s/x402check/guard

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "url": "<url>"
    },
    "name": "x402check__guard"
  }
}

Input Schema

Name	Required	Description	Default
`url`	Yes	https URL of the x402 endpoint

Schema Changelog

Changes observed during successful MCP inspections.

Changed3 schema fields changedNov 3, 2026
- addedInput schema / properties / url / description
```
Added value: +"https URL of the x402 endpoint"
```
- addedInput schema / properties / url / format
```
Added value: +"uri"
```
- addedInput schema / required
```
Added value: +[
+  "url"
+]
```
AddedNov 2, 2026

TDQS

A4.3/5.0

Behavior4/5

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

No annotations are supplied, so the description carries the full disclosure burden and does substantial work: it reveals the paid nature ($0.01/call), the settlement asset and chain (USDC on Base, eip155:8453), and the exact payment plumbing in params._meta["x402/payment"] — critical for an agent to avoid a failed call. It does not disclose failure modes, rate limits, or whether an unfunded call errors versus returns a payment challenge.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the capability, then the differentiator, then cost and transport details in a logical order, with nothing gratuitous. The price is stated twice ('$0.01/call' and '$0.01 per call in USDC on Base'), a minor redundancy that keeps it from a 5.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a one-parameter tool with no output schema and no annotations, the description covers what is checked, the output shape (yes/no verdict), the cost, and the payment mechanism — enough for correct invocation. It lacks any indication of what happens on payment failure or what detail accompanies the verdict, a small residual gap.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% for the single 'url' parameter (documented as an HTTPS x402 endpoint URL), so the baseline is 3. The description goes beyond the schema by documenting the undeclared payment envelope in params._meta["x402/payment"], which is genuine meaning the input schema omits.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('seller due diligence before paying') and enumerates the exact checks performed: endpoint liveness, valid 402 terms, domain age and registrar via RDAP, plus a yes/no verdict. It explicitly differentiates itself from the sibling x402check__check ('Lighter than /check'), so an agent can choose without opening either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The phrase 'before paying' establishes the trigger context clearly, and 'Lighter than /check' signals the trade-off versus the heavier sibling. There is no explicit statement of when *not* to use it (e.g. when terms validation depth matters more than speed), which keeps it below a 5.

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

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