Agent Utils (x402)

by dev.workers.revenue-agent-jw.agent-utils-x402-production

x402 endpoint readiness check

x402_check

Read-onlyIdempotent

x402 endpoint validator and payment-readiness checker, useful for sellers debugging a paywall or buyers vetting an endpoint before paying. Fetches the URL unpaid, decodes the 402 challenge and grades network, USDC asset, payTo, price vs facilitator fees, EIP-712 domain, CORS and Bazaar metadata. Returns a 0-100 score and a fix list. Never pays the target. Errors: 400 JSON {error} for invalid input. PAID: $0.002 USDC per call on Base via x402 (MCP transport: retry with params._meta["x402/payment"]). Same tool over plain HTTP: GET /v1/x402/check.

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": "x402_check"
  }
}

Input Schema

Name	Required	Description	Default
`url`	Yes	https URL of the x402-protected endpoint
`method`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 22, 2026

TDQS

A4.4/5.0

Behavior5/5

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

Goes well beyond the annotations: discloses that the target is never paid, that it fetches the URL unpaid, decodes the 402 challenge, grades specific attributes, returns a 0-100 score plus a fix list, and documents the 400 error shape. It also states the price ($0.002 USDC on Base), the payment retry mechanism via params._meta["x402/payment"], and the equivalent HTTP route — all critical operational context for a paid tool.

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?

Dense and front-loaded — purpose, then behavior, then return shape, then errors, then pricing/transport. Every sentence carries information, though the pricing/transport sentence is packed enough that an agent must parse carefully.

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

Completeness5/5

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

For a paid, read-only probing tool with no output schema, the description covers the missing pieces: return format (score + fix list), error behavior, cost, retry mechanics, and a non-MCP access path. Nothing an agent needs to call it correctly is absent.

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 50%: `url` is documented in the schema, but `method` has no description in either the schema or the tool description. The description adds no semantics about what `method` controls (e.g. which HTTP verb the probe uses), so this is baseline adequacy rather than compensation for the coverage gap.

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 ('x402 endpoint validator and payment-readiness checker') and names the two concrete use cases (sellers debugging a paywall, buyers vetting before paying). No sibling tool covers anything similar, so the agent can distinguish it immediately.

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?

Explicitly frames the two scenarios in which to call it — pre-payment vetting and paywall debugging — which is strong conditional guidance. It does not name exclusions or alternatives, but no sibling overlaps meaningfully, so the gap is minor.

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

All Agent Utils (x402) tools Inspect

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