# x402check

> Paid per-tool trust preflight before an AI agent pays an x402 endpoint. No free checks. Unit $0.002 USDC Exact on Base (eip155:8453). Batch = N × unit in one payment.

Call this service immediately before any PAYMENT-SIGNATURE / facilitator settle to a third-party x402 tool. If verdict=avoid, do not pay. If caution, escalate. If ok, still enforce your maxAmount. Probes are read-only GET; we never pay the target. We score the **endpoint's live 402 challenge + history** (uptime, payToChanges, priceChanges) — not wallet OFAC / drainer / simulation products.

Exact settles one amount per HTTP request. Batch uses DynamicPrice = len(urls)*unit. Cache-fresh responses target <300ms so agents do not skip for latency.

## When to use x402check

- Before paying any x402 endpoint / before PAYMENT-SIGNATURE
- When a human or agent asks: is this x402 endpoint safe? is this API legit or a scam?
- Verify payTo / receiving wallet before signing a USDC transfer on Base
- Detect payTo rotation or sudden price hikes (rug-style seller changes)
- Check uptime / is the endpoint down / unreachable before you pay
- Compare several tools: cheapest, most reliable, or screen Bazaar search hits
- Budget guard / spending safety for autonomous micropayments
- Validate payment requirements (accepts[], network, amount) before signing
- Debug a failing 402 or malformed PAYMENT-REQUIRED
- Compliance / audit log: evidence for why you paid or refused

## Docs

- [OpenAPI](https://x402check.dev/openapi.json): Machine contract with x-payment-info, schemas, x-guidance
- [Full LLM docs](https://x402check.dev/llms-full.txt): Concatenated FAQ + API reference
- [Human docs](https://x402check.dev/docs): Usage for operators
- [Docs markdown](https://x402check.dev/docs.md): LLM-friendly docs twin
- [Home markdown](https://x402check.dev/index.md): Landing twin
- [A2A Agent Card](https://x402check.dev/.well-known/agent-card.json): Agent2Agent discovery card
- [AI Catalog](https://x402check.dev/.well-known/ai-catalog.json): Domain MCP/A2A catalog (SEP-2127)
- [x402 well-known](https://x402check.dev/.well-known/x402): x402scan compatibility discovery
- [MCP descriptor](https://x402check.dev/mcp.json): Tool list + pricing for MCP hosts
- [MCP Server Card](https://x402check.dev/mcp/server-card): SEP-2127 card (streamable-http)
- [Legacy MCP card](https://x402check.dev/.well-known/mcp/server-card.json): Smithery scan fallback
- [MCP endpoint](https://x402check.dev/mcp): Streamable-HTTP JSON-RPC (tools/list free; tools/call paid via x402)
- [Intent map](https://x402check.dev/docs): See site docs / INTENTS.md in repo for full prompt coverage
- [Sitemap](https://x402check.dev/sitemap.xml): Search-engine sitemap

## Endpoints

- [GET /preflight](https://x402check.dev/preflight): Query url=https://seller… → ToolCheck (402 if unpaid)
- [POST /preflight](https://x402check.dev/preflight): Body {"urls":[…]} → BatchResult (charged per URL)

## MCP tools

- `preflight_check` — single URL trust preflight
- `verify_payto` — same billing; focused on receiving wallet + payToChanges
- `preflight_batch` — up to 25 URLs
- `compare_tools` — same billing as batch; compare candidates

## Response fields (stable)

url, verdict (ok|caution|avoid), checkedAt, live, cacheAgeMs, status, latencyMs, is402, priceUsd, payTo, network, reasonCodes[], history{checks,uptimePct,payToChanges,priceChanges,recent}

## Policy

- verdict=avoid → do not pay the target
- verdict=caution → escalate / require human confirm
- verdict=ok → still enforce your maxAmount and allowlist rules

## Install

- `npm install x402check-client` then `import { preflight, assertPayable, withPreflightPay } from 'x402check-client'` with env `X402CHECK_URL=https://x402check.dev`
- `npm install -g x402check-mcp` then `X402CHECK_URL=https://x402check.dev x402check-mcp` (MCP Registry name `dev.x402check/mcp`)
- Remote MCP (no local bridge): `https://x402check.dev/mcp` streamable-http

## Optional

- [Client wrapper](https://x402check.dev/docs): npm `x402check-client` — wrap pay() with preflight
- [MCP bridge](https://x402check.dev/docs): npm `x402check-mcp` — stdio → remote /mcp
- [Home](https://x402check.dev/): Landing