402sentinel MCP Server

402sentinel-mcp

MCP tools that let your AI agent check an x402 counterparty's risk before it pays — and turn that risk into an enforceable wallet spending policy. Give it a payTo address, get back a 0–100 risk score + an allow / review / block decision, scored from on-chain settlement behaviour on Base (address age, facilitator-aware payer diversity, settlement maturity) + a delivery-outcome flywheel, with honest confidence/coverage.

Tools — vet the seller:

• assess_counterparty ($0.002) — risk score + decision + a ready-to-apply recommended_policy
• assess_counterparty_deep ($0.02) — same, scans more on-chain history
• recommend_policy ($0.002) — decision + wallet-ready spending policy (caps, denylist, approval)
• report_outcome (free) — after paying, report delivery to train the reliability flywheel

Tools — vet the payment itself (buyer-side):

• firewall ($0.002) — should YOUR agent make THIS payment now? Catches fraudulent routing (payTo swapped vs the address you usually pay), drain velocity, overcharge, and injection-sourced instructions. agent_id + a wallet-ownership signature are attached automatically from your configured wallet — trusted routing history with no extra steps.
• firewall_record (free) — seed your agent's payment history so the firewall has a behavioural baseline.
• firewall_outcome (free) — after a verdict, report what actually happened (fraud / legit / …) so the firewall learns which signals are predictive and downweights noisy ones (safety signals stay deterministic).

It's a thin client for the hosted service at https://402sentinel.com — the scoring model and facilitator-identification logic live server-side (closed); this package only forwards the request and pays for it, so it's open source.

Quickstart — gate a payment in 5 lines

Before your agent pays any x402 counterparty, ask the firewall; if it doesn't say allow, don't pay. No MCP needed — any x402 client works (here, Circle's):

import { GatewayClient } from "@circle-fin/x402-batching/client";
const sentinel = new GatewayClient({ chain: "base", privateKey: process.env.AGENT_KEY });

const { data } = await sentinel.pay("https://402sentinel.com/api/firewall", { method: "POST", body: {
  payment: { payto_address: target, amount, resource_url },
  context: { source: "web_content", untrusted_text: pageYouActedOn } } });   // pass what you scraped

if (data.decision !== "allow") throw new Error(`402Sentinel ${data.decision}: ${data.recommended_action}`);
// …safe to pay `target`.

That one $0.002 call catches fraudulent routing (payTo swapped vs the address you usually pay), prompt-injection payments (a payTo that appeared in untrusted_text), drains, overcharges, and sanctioned/illicit counterparties.

In an MCP framework (Claude, Cursor, …) instead, just add the server — your agent gets all 7 tools by name (see Configure below):

{ "mcpServers": { "402sentinel": { "command": "402sentinel-mcp", "env": { "CLIENT_PRIVATE_KEY": "0x…" } } } }

Install

npm i -g @kaditang/402sentinel-mcp

Configure

Add to your MCP client (Claude Desktop, Cursor, etc.):

{
  "mcpServers": {
    "402sentinel": {
      "command": "402sentinel-mcp",
      "env": {
        "CLIENT_PRIVATE_KEY": "0x...  // a Base wallet with USDC in its Circle Gateway balance"
      }
    }
  }
}

Paid calls cost from $0.002 (shallow) to $0.02 (deep), paid automatically in USDC via x402 (Circle Gateway, gas-free on Base) from the configured wallet. report_outcome is free. (CLIENT_PRIVATE_KEY is only needed for the paid tools.)

Use

The agent calls it before authorizing a payment:

assess_counterparty({
  target: { payto_address: "0x..." },
  payment_context: { amount: 10, asset: "USDC" },
  policy: { block_at_score: 70, review_at_score: 40 }
})
→ { decision: "review", risk_score: 52, confidence: 0.41, coverage: {...},
    dimensions: [...], recommendation: "...",
    recommended_policy: { action: "limit", max_payment_usdc: 5, daily_cap_usdc: 15,
                          add_to_denylist: false, require_human_approval: true } }

• block / deny → don't pay
• review / limit → cap exposure / escrow (use recommended_policy for the caps)
• allow → proceed

recommend_policy(...) returns just the decision + recommended_policy — apply max_payment_usdc / daily_cap_usdc / add_to_denylist directly to your agent wallet's spending limits. After paying, call report_outcome({ assessment_id, outcome }) to improve future scores.

Disclaimer

Algorithmic risk signal, informational only — not advice, not an endorsement, and not an accusation about any party. Scores are probabilistic estimates from limited public on-chain data and heuristics, and may misclassify. Do your own due diligence; don't rely on it as your sole basis to pay or refuse. See https://402sentinel.com/terms.

MIT.