GateCheck by LarryBuildsAI

x402 Paid-Path Health Probe

probe_x402_paid_path

Read-onlyIdempotent

Probe a public x402 paid endpoint without signing or paying, then parse the HTTP 402 challenge. Pass target plus optional expected network/asset/price to verify payment metadata and receive a deterministic health receipt.

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": {
      "target": "<target>"
    },
    "name": "probe_x402_paid_path"
  }
}

Input Schema

Name	Required	Description
`mode`	No	Probe mode for v1. Defaults to unpaid_402.
`method`	No	Safe unpaid probe method. Defaults to GET.
`target`	Yes	Specific paid endpoint URL to probe without payment.
`expected`	No	Optional expected x402 metadata such as network, asset, and priceUsd.

Output Schema

Name	Required	Description	Default
`checks`	Yes
`issues`	Yes
`target`	Yes
`healthy`	Yes
`receipt`	Yes
`observed`	Yes
`recommendedFixes`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedMay 21, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations already declare readOnlyHint and idempotentHint, but the description adds valuable context: 'without signing or paying' implies no side effects, and 'receive a deterministic health receipt' clarifies output behavior. This goes beyond the annotations without contradicting them.

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

Conciseness5/5

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

Two sentences, front-loaded with the core action, and no filler. The second sentence adds actionable details about parameters and output. Every word earns its place.

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?

The description covers the core action, input expectations, and outcome (deterministic health receipt). Output schema exists, so return values need not be spelled out. It could elaborate on mode/method options, but these are already documented in the schema, making the description sufficient for this tool's complexity.

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

Parameters3/5

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

Schema description coverage is 100%, so the baseline is 3. The description mentions 'target plus optional expected network/asset/price', which corroborates the schema but adds no new semantic detail beyond what the schema already provides.

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?

The description clearly identifies the verb ('probe'), the resource ('public x402 paid endpoint'), and distinct behavioral aspects ('without signing or paying', 'parse the HTTP 402 challenge'). It also mentions the deterministic health receipt, which sets it apart from sibling tools like scan_x402_resource.

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 description provides clear context for when to use the tool—probing a paid endpoint without payment and verifying payment metadata. It does not explicitly exclude alternatives or name sibling tools, but the intended use case is evident from the wording.

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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