LayerCall SDKs

Official clients for LayerCall — score an IP, email, phone number, domain, or a whole signup for fraud in a single call.

Both clients have zero dependencies. A trust check sits on your signup path, which is the worst place in an application to introduce a dependency tree.

Get a free API key — 1,000 lookups a month, no card required, no daily cap.

Try it without installing anything

export LAYERCALL_API_KEY=tl_live_...
npx layercall ip 8.8.8.8
npx layercall email someone@mailinator.com
npx layercall domain example.com
npx layercall user --ip 1.2.3.4 --email a@b.com

What it returns

Every endpoint returns the same shape: a 0–100 risk_score, an allow | review | block verdict, and the signals behind it.

{
  "ip": "185.220.101.1",
  "risk_score": 60,
  "verdict": "review",
  "signals": {
    "is_vpn": true,
    "is_proxy": true,
    "is_datacenter": true,
    "is_tor": true,
    "recent_abuse": false
  },
  "geo": { "country": "DE", "city": "Berlin", "asn": "AS60729" },
  "vpn_provider": null
}

Two things worth reading before you integrate

Prefer step-up over rejection. The review band starts where an ordinary commercial VPN lands, and most VPN users are ordinary customers. Send them an OTP or a 3-D Secure challenge instead of a refusal: a real user clears it in seconds, an attacker cannot, and a false positive costs friction rather than a customer. This is what Stripe Radar and Sift both converged on.

null means unknown, not "no". newly_registered is null when a TLD publishes no RDAP (.de, .ru, .ac.uk among them), and mailbox_exists is null when the mail provider does not answer honestly — Gmail and Yahoo accept mail for addresses that do not exist. Treating either as a negative finding is the specific mistake these fields exist to prevent.

Endpoints

Full reference: layercall.com/docs · OpenAPI 3.1: layercall.com/openapi.json

Testing without spending anything

Test-mode keys return deterministic synthetic data, drawn from ranges reserved for exactly this purpose — RFC 5737 addresses, example.com, the 555-01XX fiction block. Same shape and fields as production, so your assertions are real ones. They never bill, never hit live data sources, and never write to the shared reputation network.

Every fixture is documented, so you can assert on exact values rather than "did it return a number": layercall.com/docs/test-mode

MCP — call it from an AI agent

LayerCall speaks the Model Context Protocol over Streamable HTTP, so Claude Code, Claude Desktop, ChatGPT, Cursor, VS Code, Windsurf and Zed can run a fraud check mid-conversation. There is nothing to install — it is a remote server, so you add a URL and your API key:

{
  "mcpServers": {
    "layercall": {
      "url": "https://www.layercall.com/api/mcp",
      "headers": { "Authorization": "Bearer YOUR_API_KEY" }
    }
  }
}

Seven tools are exposed: score_ip, verify_email, lookup_phone, score_domain, score_device, verify_agent and score_user.

VS Code names the top-level key servers, not mcpServers. That one difference is the usual reason a copied config silently does nothing.

Per-client setup: layercall.com/docs/mcp

Framework middleware

Drop-in for the two places this usually goes. The middleware attaches req.trust and leaves the decision to you:

import { layercall } from "layercall/express";

app.post("/signup", layercall(), (req, res) => {
  if (req.trust.verdict === "block") return res.status(403).json({ error: "..." });
  if (req.trust.verdict === "review") flagForManualReview(req.trust);
  createAccount(req.body);
});

There is deliberately no autoBlock: true. A one-line install that starts rejecting people is the wrong default for a fraud tool — the failure is silent, it lands on real customers, and you find out from a support ticket.

By default it only scores POST/PUT/PATCH, because a global app.use() bills a lookup for every request including favicon.ico.

See node/src/express.ts and node/src/next.ts (scoreRequest, withTrust).

Guides

Written for someone mid-incident rather than someone shopping. Each one ends with what a naive version gets wrong — including the parts that need no LayerCall at all.

• How to stop fake signups
• How to block disposable email addresses at signup
• How to detect VPN and proxy users at signup
• How to stop free trial abuse
• How to add fraud checks without losing real customers

License

MIT