ReturnCheck — Return-policy verification for AI shopping agents

ReturnCheck verifies which return policy actually applies to this purchase. For AI shopping agents, it resolves the case with a verified verdict — not a guess.

Give it a product_url and a buyer_country and it returns a verdict (YES / YES_WITH_CONDITIONS / NO / UNKNOWN) with the exact policy clause quoted from the page, the source URL, the return window, and a confidence score. If it cannot verify a clause on the page, it returns UNKNOWN — it never invents.

Built for agent-to-agent commerce: an MCP tool plus x402-friendly micro-pricing at $0.02 per verified answer (UNKNOWN is free; a keyless free trial is available).

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Why it exists

AI agents are starting to buy things. Before they buy, they need to know if a purchase is reversible — and today no one answers "is this returnable?" in a way a machine can trust and act on. ReturnCheck is the neutral verification primitive for that: it sells to every shopping agent and competes with none of them.

Quick start

MCP (Streamable HTTP) — tool: check_return

https://returncheck.m-angelmartinez-fer.workers.dev/mcp

HTTP

curl -X POST https://returncheck.m-angelmartinez-fer.workers.dev/v1/check \
  -H "content-type: application/json" \
  -d '{"product_url":"https://store.example/p/shoe","buyer_country":"US","item_condition":"unopened"}'

If you already have the product/policy page rendered, pass it as page_html or page_text — ReturnCheck verifies against it and skips fetching (best coverage, bypasses sites that block server-side reads). It still never invents.

When that content comes from a separate policy page, also send page_source_url with its HTTP(S) URL. This preserves the supplied source in evidence.source_url and the corpus while keeping product_url as the product context. The URL is caller-declared and is not independently fetched. Without it, the existing product_url fallback remains; legacy callers should add the field when supplying a different page. Opened-product alternatives are recovered only for an explicit adjacent generic clause; ambiguous, category-specific or conflicting terms still require the normal verification path.

x402 paid calls

The paid HTTP route is the same endpoint: POST /v1/check.

To inspect the live x402 terms without consuming the free allowance, send a bodyless POST /v1/check with no PAYMENT-SIGNATURE. ReturnCheck responds with the live 402 challenge. Do not send {} or a real check body for this discovery probe.

For a paid call, base64-encode a JSON envelope in the PAYMENT-SIGNATURE header:

{
  "x402Version": 2,
  "accepted": {
    "scheme": "exact",
    "network": "eip155:8453",
    "amount": "20000",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "payTo": "0xbF428071027402E9b0cE85e22146EDdc028cEB3b",
    "maxTimeoutSeconds": 60,
    "extra": { "name": "USD Coin", "version": "2" }
  },
  "payload": {
    "signature": "0x...",
    "authorization": {
      "from": "0x...",
      "to": "0x...",
      "value": "20000",
      "validAfter": "0",
      "validBefore": "...",
      "nonce": "0x..."
    }
  },
  "extensions": {
    "payment-identifier": {
      "info": {
        "required": true,
        "id": "unique-id-16-to-128-chars"
      }
    }
  }
}

Rules:

• accepted is the full accepted payment requirement object, not a boolean.
• payload directly contains signature and authorization.
• The canonical identifier path is extensions["payment-identifier"].info.id.
• Do not copy the bazaar discovery extension into PAYMENT-SIGNATURE.
• The live 402 challenge is authoritative for current payment terms.
• A signed request enters the payment path directly; there is no need to exhaust the free allowance first.
• Replay the same paid operation with the same endpoint, body, identifier, signature and nonce. If an authorization expires before the paid call, sign a fresh authorization; that fresh authorization is then the one to replay.
• On pending, unconfirmed, HTTP 500, or another ambiguous settlement outcome, do not create a second authorization until the first outcome is reconciled.

What you get back

{
  "verdict": "YES_WITH_CONDITIONS",
  "returnable": true,
  "confidence": 0.9,
  "policy": { "merchant_return_days": 30, "return_category": "FiniteReturnWindow" },
  "evidence": {
    "source_url": "https://store.example/policies/refund-policy",
    "exact_clause": "Items may be returned within 30 days of delivery for a full refund.",
    "verified_on": "2026-08-23"
  }
}

Pricing

Verified answer (YES / NO / conditions)	$0.02
UNKNOWN	Free
Keyless free trial	a few calls/day, no signup

Discovery for agents

• OpenAPI: /openapi.json
• Plugin manifest: /.well-known/ai-plugin.json
• Agents manifest: /agents.json
• LLM manifest: /llms.txt
• MCP tool list: /mcp

Deterministic preflight

Run npm run check to validate registered work and run the full regression suite. Use npm run work:new -- ucp job-name to register new work (payment, corpus and artifact profiles are also available). All registered jobs run automatically on every push and pull request. See AGENTS.md for the permanent review routine. Registered jobs now require a review receipt bound to the exact inputs. The check also detects uncovered changed files and cross-lot corpus contamination. Delivery and historical metrics profiles provide package/snapshot and benchmark checks.

Run npm run validate before reviewing payment packages, UCP evidence or corpus changes. Three offline profiles produce PASS/FAIL, blocking errors, warnings, SHA-256 hashes and fields requiring subsequent AI review. See preflight/README.md for input contracts, limits and commands. npm test includes the preflight regression tests. A PASS is not deployment or payment authorization.

Design principles

• Never invent. Every determinate verdict carries a clause verified literally against the page. If it can't be verified, the answer is UNKNOWN.
• Frozen contract (v1.0). Fields are only ever added, never broken.
• US data first, global architecture. Runs 100% serverless on the edge (Cloudflare Workers + D1 + Workers AI).

Keywords

return policy API · returns verification · AI shopping agents · agentic commerce · MCP server · check_return · x402 · agent-to-agent payments · e-commerce returns · is this returnable · refund policy checker