X402 Micro Tollgate MCP Server

x402-micro-tollgate

Visa for AI agents that can’t hold a card.

Second-scale settlement bridge for agent traffic — the Web3 tollbooth that clears USDC micropayments and takes 0.1%.

为千万级无支付能力的 AI Agent 提供秒级过桥清算，抽成 0.1% 的 Web3 版 Visa 收费站

Security backed by Coinbase CDP. We don't touch your keys or settle payments on custom cryptography — EIP-3009 authorization nonces are single-use at the CDP facilitator (source of truth for on-chain uniqueness). The gateway hardens four buyer/seller trust surfaces: payment-proof replay/race, SSRF on URL fetch, upstream bypass (shared-secret trust header), and Base congestion / settle-latency (pending + retry same proof — never treat HTTP timeout alone as “payment failed”).

What it is

A thin self-hosted tollgate in front of your API or MCP tools. When an agent calls a paid route, it gets HTTP 402 as a price tag (not a hard deny). It pays a small USDC (or configured USDT) amount; you deliver. Default clearing is Base + USDC via Coinbase CDP; multi-network accepts are env-driven (see matrix below). Humans can still hit a free path; agents convert at the booth.

Self-host is free (MIT). Repo: github.com/kevin2003050666-coder/x402-micro-tollgate · Questions: 2767111713@qq.com

Not an official Coinbase product. Not a full agent marketplace. Not a billing SaaS. A sharp Visa-style tollbooth. Not fiat custody.

Why this exists: MANIFESTO.md — pain, engineering, on-chain proof, MIT.

Network × asset matrix

Default deploy profile: Base USDC only (dev: Base Sepolia). Enable multi with NETWORKS + ASSETS or ACCEPTS_JSON / X402_* aliases. Browser HTML 402 shows a chain + asset picker when more than one accept is configured.

USDT on EVM typically uses extra.assetTransferMethod: "permit2" (not EIP-3009). FeeSplitter production path remains Base + USDC; other chains are config stubs under contracts/deployments/.

Browser wallets

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Who it’s for

• API sellers who want agents to pay per call — without building a billing console or selling monthly seats
• Tool builders shipping paid MCP endpoints into Cursor / Claude
• Operators who want Visa-like take-rate economics (0.1%), not hosting invoices

How money works

1. Price tag — unpaid traffic gets HTTP 402 with the amount due (conversion, not rejection)
2. Pay — the agent settles a USDC micropayment in seconds via Coinbase CDP
3. Unlock — the tollgate proxies to your upstream; you keep ~99.9%, protocol take 0.1%

No protocol monthly fee. Monetization is the toll — like interchange on card rails.

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1-minute quickstart

Requires Node.js 22+.

git clone https://github.com/kevin2003050666-coder/x402-micro-tollgate
cd x402-micro-tollgate && cp .env.example .env
# set CDP_API_KEY_ID, CDP_API_KEY_SECRET, X402_PAY_TO (optional: PUBLIC_BASE_URL, UPSTREAM_URL)
npm i && npm start
# curl http://127.0.0.1:8402/health   → 200
# curl http://127.0.0.1:8402/x402/discover → 200 (free agent yellow pages)
# curl http://127.0.0.1:8402/v1/quote → 402
# curl "http://127.0.0.1:8402/v1/fetch-md?url=https://example.com" → 402 (paid HTML→Markdown demo)

npx one-liners (no clone):

npx x402-micro-tollgate@0.3.3
npx x402-micro-tollgate@0.3.3 --seller 0xYourReceivingAddress --stdio

--seller / -s sets X402_PAY_TO before boot (env vars still work). Default without --stdio is HTTP + /mcp on port 8402.

Agent / crawler docs: llms.txt (also GET /llms.txt and GET /.well-known/llms.txt) · OpenAPI 3.1: docs/openapi.yaml · well-known: GET /.well-known/x402.json, GET /.well-known/agent-card.json

Alternative one-liner: docker compose up --build

Without CDP keys the process runs in demo mode (protocol-shaped 402 / MCP PaymentRequired, no on-chain settle).

Cursor mcp.json:

{
  "mcpServers": {
    "x402-micro-tollgate": {
      "url": "http://127.0.0.1:8402/mcp"
    }
  }
}

Stdio:

{
  "mcpServers": {
    "x402-micro-tollgate": {
      "command": "npx",
      "args": [
        "x402-micro-tollgate@0.3.3",
        "--seller",
        "0xYourReceivingAddress",
        "--stdio"
      ],
      "env": {
        "CDP_API_KEY_ID": "...",
        "CDP_API_KEY_SECRET": "...",
        "PUBLIC_BASE_URL": "https://your.public.host"
      }
    }
  }
}

(X402_PAY_TO in env still works if you omit --seller.)

Library drop-in (permissionless seller)

import express from "express";
import { x402Tollgate } from "x402-micro-tollgate";

const app = express();
app.use("/v1", await x402Tollgate({ seller: process.env.SELLER! }));

Or set SELLER / X402_SELLER in .env and run npm start. See Environment for the $10 threshold, factory address, and fee-release details.

Buyer / Agent client

Thin TypeScript helper that wraps official @x402/fetch + @x402/evm ExactEvmScheme. On HTTP 402 it parses PAYMENT-REQUIRED, checks budgets, signs EIP-3009 once, and retries once with PAYMENT-SIGNATURE (never loops).

npm i x402-micro-tollgate@0.3.3

import { createX402Fetch } from "x402-micro-tollgate/client";
const fetch402 = createX402Fetch({ privateKey: process.env.BUYER_KEY as `0x${string}` });
const res = await fetch402("https://x402-micro-tollgate.onrender.com/v1/quote");

Defaults: maxSingleSpendUsdc = 0.05, maxTotalSpendUsdc = 1.00 (clear Error if exceeded). Circuit breaker (before sign): max 10 paid 402s / 0.05 USDC per rolling 60s, plus fingerprint dead-loop halt (maxPaidRequestsPerMinute, maxSpendUsdcPerMinute, enableFingerprintBreaker). Hot-wallet warning: keep only ~$5–$10 USDC on the signing key — treat it as an agent spend faucet, not a treasury.

Human-delegated agent credit (CLI)

Thin PoC: Human sets B_max → Agent loops createX402Fetch against a paid URL (auto 402 → pay once → retry). Chrome / Telegram / Session Key / Passkey UI are deferred.

# SAFETY: fund BUYER_PRIVATE_KEY with ≤ $5–$10 USDC only. Never commit keys.
export BUYER_PRIVATE_KEY=0xYourHotWalletKey
# optional: TARGET_URL MAX_SINGLE_USDC MAX_TOTAL_USDC ROUNDS
npm run poc:buyer-agent
# or: npx tsx scripts/buyer-agent-poc.ts

The script imports the local client (../src/client) so repo CI does not need a live chain pay. For a live demo against the published package, swap the import to x402-micro-tollgate/client (same API as 0.3.2+). Each round prints status, autoPaid, and sessionSpendUsdc on stdout; the safety banner goes to stderr.

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Deploy

Uses render.yaml: Node 22, npm start, health /health, env names from .env.example. Set CDP_API_KEY_ID, CDP_API_KEY_SECRET, and X402_PAY_TO in the dashboard for live settlement; set PUBLIC_BASE_URL to your https://….onrender.com origin for Bazaar.

Ops bump: redeploy discover + well-known (force Render GitHub auto-deploy so production picks up GET /x402/discover, GET /.well-known/x402.json, GET /.well-known/agent-card.json, and MCP fetch_md). If auto-deploy does not fire within a few minutes after this lands on main, use the Render dashboard → Manual Deploy → Deploy latest commit.

Self-host production: Docker — docker compose up --build (see Dockerfile / docker-compose.yml).

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Environment

Permissionless seller + $10 threshold (0.3.0)

0.3.0: set SELLER (or use x402Tollgate({ seller })) and FACTORY_ADDRESS for ≥ $10 CREATE2 routing. No MERCHANTS_JSON required.

x402 exact + EIP-3009 only credits payTo — it does not execute FeeSplitter / factory code and does not split in the same transaction. For ≥ $10: set FACTORY_ADDRESS to the operator-deployed factory (Base reference: contracts/deployments/base.json), call getOrCreate(seller) before the first such settle, then release() later (99.9% / 0.1%). Address typos send funds to the wrong place — the gateway checksum-validates SELLER at startup. Do not hardcode private keys or operator secrets in source.

Merchant registry (optional hosted multi-tenant)

Operator FEE_COLLECTOR is fixed: 0xa922F38041B5ee227c96A547F106F1330447e30E. Each merchant gets their own FeeSplitter (seller = merchant wallet, feeCollector = operator, feeBps = 10). The registry maps merchantId → splitter address (payTo) + seller for display. When SELLER is set, the registry is optional; ?merchant= still works if you provide MERCHANTS_JSON.

Register a merchant:

1. Deploy FeeSplitter with seller = merchant wallet, feeCollector = 0xa922F38041B5ee227c96A547F106F1330447e30E, feeBps = 10, and the chain’s native USDC as asset.
2. Add an entry to MERCHANTS_JSON (or merchants.json / copy from merchants.example.json):

   {
     "acme": {
       "seller": "0xMerchantWallet…",
       "payTo": "0xDeployedFeeSplitter…",
       "label": "Acme API"
     }
   }
   

3. Call gated APIs with ?merchant=acme or header x-merchant-id: acme (case-insensitive). Agents SHOULD always send merchant id. If omitted, the gateway falls back to DEFAULT_MERCHANT (demo) — that means traffic (and USDC) can silently land on the demo FeeSplitter. Set REQUIRE_MERCHANT=true to reject missing merchant with 400 { "error": "merchant_required" }. Unknown merchant on gated paths → 400 { "error": "unknown_merchant" }.
4. Free listing: GET /merchants (also /v1/merchants).
5. Agent yellow pages: GET /x402/discover (alias GET /discover) — stable JSON catalog derived from the same registry / SELLER / demo. JSON config stays supported; there is no on-chain Registry.sol $5 stake in this release.

Note: The Base demo splitter has seller = feeCollector = operator — fine for demo. Real merchants need their own splitter with their wallet as seller.

CDP createX402Server uses a single global payTo for SDK init (X402_PAY_TO or the default merchant splitter). Per-request merchant routing rewrites PAYMENT-REQUIRED accepts[].payTo to the resolved FeeSplitter (same pattern as the https resource.url rewrite).

If X402_PAY_TO is still an EOA and you only have one merchant, behavior stays simple. Multi-merchant production should point each registry payTo at a deployed splitter — x402/exact credits that splitter via EIP-3009; call release() later (manually or via the optional keeper) to send 99.9% / 0.1%. Same contract on Base / Arbitrum / Polygon — see the multi-chain FeeSplitter matrix. This is receive → later release(), not an atomic same-transaction split and not OpenZeppelin PaymentSplitter.

Discovery (live) + liquidity roadmap (planned)

Ship now — Discovery only. Free route GET /x402/discover (alias /discover) returns agent-readable yellow pages from existing sources (MERCHANTS_JSON / merchants file / SELLER / built-in demo) + PUBLIC_BASE_URL. No 402. Example shape:

{
  "version": 1,
  "network": "eip155:8453",
  "updatedAt": "2026-09-03T00:00:00.000Z",
  "source": "merchants",
  "services": [{
    "id": "demo",
    "label": "demo (operator is also seller)",
    "endpoint": "https://your-host/v1/quote?merchant=demo",
    "mcp": "https://your-host/mcp",
    "capabilities": ["quote", "proxy", "fetch-md"],
    "price": "$0.001",
    "asset": "USDC",
    "payTo": "0x…",
    "seller": "0x…",
    "status": "demo"
  }]
}

status is health-honest: live only when CDP facilitator credentials + payTo are configured; otherwise demo (or config when accepts are non-live). This is not an on-chain Agent Registry.

Planned (documented only — do not treat as shipped):

Full notes: docs/ROADMAP-LIQUIDITY.md. No depositBounty / claimBounty on FeeSplitter and no fake “live” cross-chain clearing claims in this release.

发现层已上线（GET /x402/discover）；闪电流动性池与反向赏金仅为规划，见 roadmap。

Gas vs micropayment floor (optional)

Micropayments ($0.001–$0.01) assume Base low fees. When L2 gas spikes, estimated settle cost can eat most of a tiny payment. Opt in with X402_DYNAMIC_MIN_ENABLED=true: a cached Base baseFee oracle (TTL 15–60s, no RPC spam) estimates gas USD (gasUsedEstimate * baseFee * X402_ETH_USD) and, if that exceeds X402_GAS_COST_MAX_FRACTION of the payment (default 50%), bumps the displayed/enforced minimum accept amount and may raise feeFreeBelow so FeeSplitter+release() isn’t used until larger amounts. Default is OFF so demo $0.001 still works under normal conditions. Operators can also set a static X402_MIN_PRICE_USDC. Current effective mins are on GET /health → gasFloor.

Security (gateway hardening)

Four defenses buyers and sellers should know about:

1. Payment signature replay / race — Idempotency key = SHA-256(PAYMENT-SIGNATURE). An in-process mutex + PaymentDedupeStore (memory today; Redis-shaped interface) does set-if-absent before upstream. Concurrent losers get 409 { "error": "payment_already_used" }. Durable mark happens only after settle success; verify failure releases the pending reservation so honest retries are not bricked.
2. SSRF on /v1/fetch-md — Only http/https; DNS resolve rejects private/bogon/link-local/metadata; DNS is re-checked before fetch (rebinding defense); redirects are disabled.
3. Upstream bypass — Optional UPSTREAM_SHARED_SECRET: after payment, proxy injects X-Tollgate-Secret / X-Tollgate-Paid / X-Tollgate-Timestamp. Your upstream must require them (see snippet below). This is a shared-secret MVP, not mTLS.
4. Base congestion / settle latency — X402_SETTLE_TIMEOUT_MS (default 3 minutes) is separate from the short verify budget. If settle is still in progress when the waiter expires → 202 { "error": "payment_pending", "retry_with_same_proof": true }. Do not create a new payment and do not treat the buyer as failed solely because HTTP timed out — retry the same proof; the gateway resumes without double-settling.

CDP facilitator is a single-vendor settle dependency by default; see SECURITY.md for X402_FACILITATOR_URL (alternate facilitator when available — no multi-facilitator routing yet).

Payment proof idempotency + settle pending

CDP x402 exact + EIP-3009 authorizations are single-use at the facilitator (nonce). The gateway additionally tracks each proof fingerprint as pending → settled → consumed:

Process-local only by default (restart clears). Facilitator remains authoritative for on-chain nonce uniqueness.

Upstream trust header (Express example)

import { createHmac, timingSafeEqual } from "node:crypto";
import type { RequestHandler } from "express";

const SECRET = process.env.UPSTREAM_SHARED_SECRET!;

export const requireTollgate: RequestHandler = (req, res, next) => {
  const secret = req.header("x-tollgate-secret") ?? "";
  const paid = req.header("x-tollgate-paid") ?? "";
  const ts = req.header("x-tollgate-timestamp") ?? "";
  const expected = createHmac("sha256", SECRET)
    .update(`${ts}.${req.method.toUpperCase()}.${req.path}`, "utf8")
    .digest("hex");
  const okSecret =
    secret.length === SECRET.length &&
    timingSafeEqual(Buffer.from(secret), Buffer.from(SECRET));
  const okPaid =
    paid.length === expected.length &&
    timingSafeEqual(Buffer.from(paid), Buffer.from(expected));
  if (!okSecret || !okPaid) {
    res.status(401).json({ error: "tollgate_required" });
    return;
  }
  next();
};

// app.use(requireTollgate); // reject public direct hits

Or import verifyUpstreamTrustHeaders from x402-micro-tollgate in your upstream process.

Optional FeeSplitter release keeper

Scaffold in src/keeper.ts. Off by default (KEEPER_ENABLED unset/false). When enabled, every KEEPER_INTERVAL_MS (default 1h) it checks USDC balances of registry payTo FeeSplitter addresses and calls release() when balance ≥ KEEPER_MIN_USDC (default $1).

Warning: Gas for release() can exceed the 0.1% operator fee on sub-cent payments — hence the min-balance gate. Do not turn this on by default on Render. Prefer KEEPER_DRY_RUN=true (logs keeper_would_release) before using a real KEEPER_PRIVATE_KEY. Never commit keys.

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Bazaar discovery (agents find sellers)

Bazaar is the x402 discovery catalog.

• HTTP: createX402Server auto-injects bazaar; we override with discoverable: true, descriptions, and input/output schemas (GET /v1/quote + gated prefix proxies).
• MCP: x402ResourceServer does not auto-declare Bazaar — we register bazaarResourceServerExtension and pass declareDiscoveryExtension({ toolName, inputSchema, … }) on get_quote / proxy_request / fetch_md. Resource URL is PUBLIC_BASE_URL/mcp (a real http(s) URL, not a display name).
• Origin well-known: GET /.well-known/x402.json (alias /.well-known/x402) mirrors discover + lists live paid HTTP/MCP resources for facilitator-independent crawlers.

To appear in Bazaar:

1. Set PUBLIC_BASE_URL to a public https origin (localhost listings are a no-op for real crawlers).
2. Run with live CDP credentials + X402_PAY_TO.
3. Complete one successful settlement through the CDP facilitator (empty-body probes on gated routes return 402, not 400).

Launch tip: share your /mcp or /v1/quote URL in Discord #x402 after that first settlement.

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Pay in browser (Smart Wallet)

When a browser hits a gated route (Accept: text/html + Mozilla UA), the gateway returns a thin HTML paywall instead of JSON. Agents / MCP / curl keep the JSON 402 body.

What you get

1. Connect / create a Coinbase Smart Wallet via the official @x402/paywall EVM UI (Coinbase Wallet connector — Passkey Smart Wallet, no MetaMask required).
2. Sign the x402 exact EIP-3009 payment on Base (or Base Sepolia in development) and retry with PAYMENT-SIGNATURE.
3. Get USDC (optional): when server CDP keys are set, the paywall shows a Get USDC button that calls POST /x402/session-token and opens Coinbase Onramp. Apple Pay / card appear only if Onramp supports them for your domain — this repo does not fake Apple Pay outside Onramp, and does not claim a guaranteed “10 second Apple Pay” without Portal production access.

Setup (buyer UX)

# .env — server secrets stay on the host
CDP_API_KEY_ID=…
CDP_API_KEY_SECRET=…
X402_PAY_TO=0x…          # or SELLER=0x…

# Public client key only (browser-safe)
CDP_CLIENT_API_KEY=…     # from portal.cdp.coinbase.com

# Optional but recommended for live demo / Bazaar
PUBLIC_BASE_URL=https://your.host
X402_ENVIRONMENT=development   # Base Sepolia (eip155:84532)
# X402_ENVIRONMENT=production  # Base mainnet (eip155:8453)

Honesty / production notes

• MVP networks: Base Sepolia (development) and Base mainnet (production / NETWORK=eip155:8453).
• Onramp production: enable Onramp in CDP Portal, allowlist your domain, and complete any Apple Pay domain verification Coinbase requires. Until then, Smart Wallet pay + sign + retry still works; Get USDC may error or omit card rails.
• CSP: the paywall ships inline scripts (same as upstream @x402/paywall). Prefer not to set a strict script-src without nonces on 402 HTML responses.
• Security: wallet private keys never touch the frontend; only the public client key is embedded. Session tokens are minted server-side.

Try it: open https://your-host/v1/quote in Chrome after configuring the keys above.

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What it does

Agents / clients
   ├─ HTTP  /v1/*          → x402 402 JSON (agents) or Smart Wallet HTML paywall (browsers)
   ├─ GET   /v1/fetch-md   → paid HTML→Markdown demo (same x402 gate)
   ├─ GET   /x402/discover → free agent yellow pages (alias /discover; from merchants JSON)
   ├─ GET   /.well-known/x402.json → free Bazaar-friendly origin manifest (alias /.well-known/x402)
   ├─ GET   /.well-known/agent-card.json → free agent card (alias /.well-known/agent.json)
   ├─ GET   /llms.txt      → free AI-crawler summary (alias /.well-known/llms.txt)
   ├─ GET   /openapi.yaml  → free OpenAPI 3.1 (alias /docs/openapi.yaml)
   ├─ POST  /x402/session-token → free Onramp session token (when CDP server keys set)
   ├─ GET   /merchants     → free merchant registry (id, label, seller, payTo)
   ├─ GET   /health        → free (+ paywall config flags)
   ├─ GET   /              → developer landing (EN / 中文)
   └─ MCP   /mcp           → server_info (free), get_quote + proxy_request + fetch_md (paid + bazaar)

CLI: npx x402-micro-tollgate@0.3.3 | --seller 0x… / -s | --stdio | --port N

Agent SEO: llms.txt · docs/openapi.yaml

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Publishing

Package identity (must stay in sync):

• package.json mcpName = io.github.kevin2003050666-coder/x402-micro-tollgate
• server.json name = same string

Flow (needs tokens on a machine that has them — not this VM):

1. Public GitHub mirror at kevin2003050666-coder/x402-micro-tollgate
2. npm publish (or tag v* → .github/workflows/publish-mcp.yml)
3. mcp-publisher publish (OIDC) → official MCP Registry
4. PulseMCP auto-ingests from the official registry — do not submit to PulseMCP directly

Update server.json remotes[0].url to your real public /mcp before publishing remotes.

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Tests

npm test

No live CDP credentials required.

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License

MIT · See CONTRIBUTING.md · SECURITY.md