SPORE x402 Attestation

endpoint-check

Check an x402 endpoint before paying it: fetch the unpaid 402 challenge of any x402 URL and verify it is payable and safe - HTTP 402, a parseable x402 v1/v2 challenge, network, asset, payTo, amount, whether the advertised resource URL is the URL you actually called, manifest consistency (/.well-known/x402.json), header-size overflow risk for Node clients, and a signed pay / caution / avoid verdict. Read-only: we never send a payment.

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": "endpoint-check"
  }
}

Input Schema

Name	Required	Description	Default
`url`	Yes	x402 URL to check before paying it.

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 21, 2026

TDQS

A3.9/5.0

Behavior4/5

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

With no annotations, the description carries the full burden and does so well: it states read-only behavior, that no payment is sent, the specific risk checks (header-size overflow, manifest consistency, resource URL match), and a signed pay/caution/avoid verdict. It omits error behavior, rate limits, and auth needs, so it is strong but not exhaustive.

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?

It is front-loaded with the purpose before the enumeration, and each list item is substantive rather than filler. The single long comma-chained sentence is dense and could be broken up for scanability, but nothing is wasted.

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?

With no annotations and no output schema, the description compensates by describing the verdicts returned (pay/caution/avoid) and the checks performed. It does not describe the shape of the signed verdict, leaving a small gap, but overall an agent has enough to call the tool correctly and interpret results.

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?

The single `url` parameter has 100% schema description coverage, so the schema already documents it. The description adds only the implicit notion that the URL must be an x402 endpoint via "any x402 URL," which is minimal beyond the schema. Baseline 3 is appropriate for high coverage.

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

Purpose4/5

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 endpoint before paying it") and then enumerates exactly what it validates, so the agent knows precisely what the tool does. It stops short of differentiating itself from closely related siblings like x402_preflight and x402_attest, which likely overlap in scope.

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 "before paying it" framing gives clear situational guidance and "Read-only: we never send a payment" clarifies a key constraint. However, it never names or excludes alternatives such as x402_preflight or dns-preflight, so an agent facing those siblings has no routing guidance.

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

All SPORE x402 Attestation tools Inspect

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