Facilitator

What is a Facilitator?

Think of a facilitator as your payment assistant - it sits between clients and servers, verifying payments and settling them on-chain so you don’t have to deal with blockchain nodes, gas fees, or settlement complexity. The simple version: Clients sign payments, facilitators verify them and post them to the blockchain. Everyone’s happy.

Why Use a Facilitator?

Zero Blockchain Hassle

No need to run nodes, manage RPC endpoints, or worry about gas prices

Instant Verification

Check if payments are valid in milliseconds without waiting for blocks

Standardized Flow

Consistent verification and settlement across all x402 implementations

No Custody Risk

Facilitators never hold your funds - they just execute signed authorizations

How It Works

The facilitator handles two critical jobs in the x402 payment flow:

Payment Verification

Client sends a signed payment. Facilitator checks:

Is the signature valid?
Does the amount match what’s required?
Has this nonce been used before?
Is there enough balance?

On-Chain Settlement

After verification, facilitator submits the payment to the blockchain:

Executes the EIP-3009 transferWithAuthorization
Pays the gas fees (not you!)
Returns transaction confirmation

The 402.cat Facilitator

We’ve launched our own facilitator built in Rust with x402-rs. It’s fast, reliable, and handles all the payment complexity for you.

Endpoints

Our facilitator exposes these HTTP endpoints:

Endpoint	Method	Purpose
`/verify`	POST	Verify a payment signature without settling
`/settle`	POST	Verify and settle a payment on-chain
`/health`	GET	Check if facilitator is healthy
`/supported`	GET	List supported networks and tokens

Example: Verifying a Payment

POST https://facilitator.402.cat/verify
Content-Type: application/json

{
  "version": 2,
  "network": "eip155:84532",
  "authorization": {
    "from": "0xUserWallet...",
    "to": "0xRecipient...",
    "value": "100000",  // $0.10 USDC
    "validAfter": 0,
    "validBefore": "115792089...",
    "nonce": "0xUnique...",
    "v": 27,
    "r": "0x...",
    "s": "0x..."
  }
}

Response (Valid):

{
  "isValid": true,
  "payer": "0xUserWallet..."
}

Response (Invalid):

{
  "isValid": false,
  "invalidReason": "INSUFFICIENT_BALANCE",
  "invalidReasonDetails": "Account balance is 0.05 USDC, required 0.10 USDC",
  "payer": "0xUserWallet..."
}

Example: Settling a Payment

POST https://facilitator.402.cat/settle
Content-Type: application/json

{
  "version": 2,
  "network": "eip155:84532",
  "authorization": {
    // ... same payment structure as verify
  }
}

Response (Success):

{
  "success": true,
  "network": "eip155:84532",
  "transaction": "0xTransactionHash...",
  "payer": "0xUserWallet..."
}

Response (Failure):

{
  "success": false,
  "network": "eip155:84532",
  "transaction": "",
  "errorReason": "INVALID_SIGNATURE",
  "errorReasonDetails": "Signature verification failed",
  "payer": "0xUserWallet..."
}

Payment Flow with Facilitator

Here’s how a typical x402 payment flows through the facilitator:

Security Model

Can facilitators steal funds?

No. Facilitators can only execute the exact authorization you signed. They cannot:

Change the amount
Change the recipient
Reuse signatures (nonce protection)
Access funds beyond what you authorized

What if the facilitator goes down?

Your funds are safe. The worst case is that:

Payments won’t verify temporarily
Settlements won’t execute
You can switch to another facilitator

Your signed authorizations remain valid and can be submitted by any facilitator or even directly on-chain.

Can facilitators see my private keys?

Never. Facilitators only see:

Your wallet address (public)
Signed authorizations (public data + signature)
Transaction amounts (transparent)

Private keys never leave your device.

What about MEV and front-running?

Facilitators submit transactions on your behalf, which means:

They choose gas prices
They can see pending payments
Settlement timing is in their control (usually 300ms delay)

For MEV-sensitive operations, use shielded swaps ($1 fee) which use private mempools.

Multiple Facilitators

402.cat supports round-robin across multiple facilitators for high availability:

Facilitator	Network	Status	Special Features
402.cat	Base, Base Sepolia	Primary	Our in-house Rust implementation
PayAI	Multi-chain	Active	Solana, Base, Polygon support
Coinbase CDP	Base	Active	Enterprise-grade (API key required)

If one facilitator is down, the system automatically tries the next.

Building with Facilitators

Option 1: Use Our CLI (Easiest)

# CLI handles everything automatically
httpcat buy MOON 0.10

# Behind the scenes:
# 1. Gets 402 response with facilitator info
# 2. Signs payment locally
# 3. Retries request with payment header
# 4. Server uses facilitator to verify/settle

Option 2: Direct Integration

import { x402Client } from '@402/client';

const client = new x402Client({
  privateKey: process.env.PRIVATE_KEY,
  facilitator: 'https://facilitator.402.cat'
});

// Client handles 402 → sign → verify → settle flow
const response = await client.post('/entrypoints/token_buy_0_10/invoke', {
  identifier: 'MOON',
  amount: 0.10
});

Option 3: Manual Facilitator Calls

// 1. Get payment requirements
const initial = await fetch('https://agent.402.cat/tokens/buy', {
  method: 'POST',
  body: JSON.stringify({ symbol: 'MOON', amount: 0.10 })
});

if (initial.status === 402) {
  const { cost, facilitator, nonce } = await initial.json();

  // 2. Sign payment
  const signature = signEIP3009Authorization({
    from: myWallet,
    to: facilitator,
    value: parseUnits(cost, 6), // USDC has 6 decimals
    nonce
  });

  // 3. Retry with payment
  const response = await fetch('https://agent.402.cat/tokens/buy', {
    method: 'POST',
    headers: {
      'PAYMENT-SIGNATURE': btoa(JSON.stringify({
        version: 2,
        network: 'eip155:84532',
        authorization: signature
      }))
    },
    body: JSON.stringify({ symbol: 'MOON', amount: 0.10 })
  });
}

Error Handling

The facilitator returns structured errors to help debug payment issues:

Error Reason	Description	Fix
`INSUFFICIENT_BALANCE`	Not enough USDC in wallet	Top up USDC balance
`INVALID_SIGNATURE`	Signature doesn’t match	Check signing logic
`NONCE_ALREADY_USED`	Payment already processed	Get fresh nonce from 402 response
`AMOUNT_MISMATCH`	Signed amount ≠ required amount	Sign correct amount
`NETWORK_MISMATCH`	Wrong blockchain network	Use correct CAIP-2 network ID
`ONCHAIN_FAILURE`	Blockchain rejected transaction	Check gas, balance, network status

Performance

Our facilitator is optimized for speed:

Verification: < 100ms (signature + balance check)
Settlement: ~2-5 seconds (depends on blockchain)
Uptime: 99.9% target
Rate limits: 1000 requests/min per IP

Supported Networks

Check which networks a facilitator supports:

curl https://facilitator.402.cat/supported

Response:

{
  "networks": [
    {
      "caip2": "eip155:84532",
      "name": "Base Sepolia",
      "nativeCurrency": "ETH",
      "tokens": [
        {
          "symbol": "USDC",
          "address": "0x036CbD53842c5426634e7929541eC2318f3dCF7e",
          "decimals": 6
        }
      ]
    },
    {
      "caip2": "eip155:8453",
      "name": "Base",
      "nativeCurrency": "ETH",
      "tokens": [
        {
          "symbol": "USDC",
          "address": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
          "decimals": 6
        }
      ]
    }
  ]
}

Next Steps

x402 Protocol

Learn how the full payment protocol works

CLI Installation

Get started with httpcat CLI (handles facilitators automatically)

API Reference

Explore all paid endpoints

Fee Structure

Understand x402 and trading fees

Facilitators make x402 payments feel instant and gasless from the user’s perspective. They handle all the blockchain complexity so you can focus on building great products.

Getting Started

httpcat-cli

MCP Server

Core Concepts

What is a Facilitator?

Why Use a Facilitator?

Zero Blockchain Hassle

Instant Verification

Standardized Flow

No Custody Risk

How It Works

The 402.cat Facilitator

Endpoints

Example: Verifying a Payment

Example: Settling a Payment

Payment Flow with Facilitator

Security Model

Multiple Facilitators

Building with Facilitators

Option 1: Use Our CLI (Easiest)

Option 2: Direct Integration

Option 3: Manual Facilitator Calls

Error Handling

Performance

Supported Networks

Next Steps

x402 Protocol

CLI Installation

API Reference

Fee Structure

Getting Started

httpcat-cli

MCP Server

Core Concepts

​What is a Facilitator?

​Why Use a Facilitator?

Zero Blockchain Hassle

Instant Verification

Standardized Flow

No Custody Risk

​How It Works

​The 402.cat Facilitator

​Endpoints

​Example: Verifying a Payment

​Example: Settling a Payment

​Payment Flow with Facilitator

​Security Model

​Multiple Facilitators

​Building with Facilitators

​Option 1: Use Our CLI (Easiest)

​Option 2: Direct Integration

​Option 3: Manual Facilitator Calls

​Error Handling

​Performance

​Supported Networks

​Next Steps

x402 Protocol

CLI Installation

API Reference

Fee Structure

What is a Facilitator?

Why Use a Facilitator?

How It Works

The 402.cat Facilitator

Endpoints

Example: Verifying a Payment

Example: Settling a Payment

Payment Flow with Facilitator

Security Model

Multiple Facilitators

Building with Facilitators

Option 1: Use Our CLI (Easiest)

Option 2: Direct Integration

Option 3: Manual Facilitator Calls

Error Handling

Performance

Supported Networks

Next Steps