fast-protocol

Fast Protocol — Instant Token Swaps

Fast Protocol enables instant token swaps on Ethereum mainnet. There are two swap paths:

1. ERC-20 swaps — gasless, signed EIP-712 intents submitted to a relayer
2. ETH swaps — direct transactions routed through FAST RPC

Both paths settle through Uniswap V3 pools and benefit from mev-commit preconfirmations for guaranteed execution.

Architecture

ERC-20 Swap Flow:
  User signs EIP-712 intent
    → POST /fastswap (relayer)
      → Relayer executes on Settlement Contract
        → Uniswap V3 swap
          → Tokens delivered to user

ETH Swap Flow:
  User sends ETH
    → POST /fastswap/eth
      → FAST RPC routes through mev-commit
        → Settlement Contract wraps ETH → swaps via Uniswap V3
          → Tokens delivered to user

Contract Addresses

Contract	Address
Settlement	0x084C0EC7f5C0585195c1c713ED9f06272F48cB45
Permit2	0x000000000022D473030F116dDEE9F6B43aC78BA3
Uniswap V3 Quoter V2	0x61fFE014bA17989E743c5F6cB21bF9697530B21e
WETH	0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2

Getting a Quote

Before swapping, get a quote from Uniswap V3 Quoter V2. This is an on-chain call, so use any Ethereum RPC (or FAST RPC).

curl Example — Quote

# Encode the quoteExactInputSingle call
# Function: quoteExactInputSingle((address,address,uint256,uint24,uint160))
# This example quotes swapping 1 WETH for USDC

curl -X POST https://fastrpc.mev-commit.xyz \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_call",
    "params": [{
      "to": "0x61fFE014bA17989E743c5F6cB21bF9697530B21e",
      "data": "0xc6a5026a000000000000000000000000c02aaa39b223fe8d0a0e5c4f27ead9083c756cc2000000000000000000000000a0b86991c6218b36c1d19d4a2e9eb0ce3606eb480000000000000000000000000000000000000000000000000de0b6b3a764000000000000000000000000000000000000000000000000000000000000000001f40000000000000000000000000000000000000000000000000000000000000000"
    }, "latest"],
    "id": 1
  }'

JavaScript Example — Quote with viem

import { createPublicClient, http, parseAbi, parseEther } from "viem";
import { mainnet } from "viem/chains";

const client = createPublicClient({
  chain: mainnet,
  transport: http("https://fastrpc.mev-commit.xyz"),
});

const quoterAbi = parseAbi([
  "function quoteExactInputSingle((address tokenIn, address tokenOut, uint256 amountIn, uint24 fee, uint160 sqrtPriceLimitX96)) external returns (uint256 amountOut, uint160 sqrtPriceX96After, uint32 initializedTicksCrossed, uint256 gasEstimate)",
]);

const WETH = "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2";
const USDC = "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48";

const [amountOut] = await client.readContract({
  address: "0x61fFE014bA17989E743c5F6cB21bF9697530B21e",
  abi: quoterAbi,
  functionName: "quoteExactInputSingle",
  args: [{
    tokenIn: WETH,
    tokenOut: USDC,
    amountIn: parseEther("1"),
    fee: 500, // 0.05% pool
    sqrtPriceLimitX96: 0n,
  }],
});

console.log("1 WETH =", Number(amountOut) / 1e6, "USDC");

ERC-20 Swap Flow (Gasless)

ERC-20 swaps are gasless for the user. The relayer pays gas and executes the swap on your behalf. You just sign an EIP-712 intent.

Step 1: Approve Permit2

The token you're swapping must be approved for Permit2. This is a one-time transaction per token.

import { erc20Abi } from "viem";

const approvalHash = await walletClient.writeContract({
  address: TOKEN_ADDRESS,
  abi: erc20Abi,
  functionName: "approve",
  args: [
    "0x000000000022D473030F116dDEE9F6B43aC78BA3", // Permit2
    2n ** 256n - 1n, // max approval
  ],
});

Step 2: Sign EIP-712 Intent

The intent specifies what you want to swap and the minimum amount you'll accept.

const domain = {
  name: "FastSwap",
  version: "1",
  chainId: 1,
  verifyingContract: "0x084C0EC7f5C0585195c1c713ED9f06272F48cB45",
};

const types = {
  SwapIntent: [
    { name: "sender", type: "address" },
    { name: "tokenIn", type: "address" },
    { name: "tokenOut", type: "address" },
    { name: "amountIn", type: "uint256" },
    { name: "minAmountOut", type: "uint256" },
    { name: "fee", type: "uint24" },
    { name: "nonce", type: "uint256" },
    { name: "deadline", type: "uint256" },
  ],
};

const intent = {
  sender: account.address,
  tokenIn: WETH,
  tokenOut: USDC,
  amountIn: parseEther("1"),
  minAmountOut: 2400_000000n, // 2400 USDC (6 decimals)
  fee: 500,
  nonce: BigInt(Date.now()),
  deadline: BigInt(Math.floor(Date.now() / 1000) + 300), // 5 min
};

const signature = await walletClient.signTypedData({
  domain,
  types,
  primaryType: "SwapIntent",
  message: intent,
});

Step 3: Submit to Relayer

curl -X POST https://fastrpc.mev-commit.xyz/fastswap \
  -H "Content-Type: application/json" \
  -d '{
    "intent": {
      "sender": "0xYourAddress",
      "tokenIn": "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
      "tokenOut": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
      "amountIn": "1000000000000000000",
      "minAmountOut": "2400000000",
      "fee": 500,
      "nonce": "1709500000000",
      "deadline": "1709500300"
    },
    "signature": "0x YOUR_EIP712_SIGNATURE"
  }'

Response:

{
  "txHash": "0x...",
  "status": "preconfirmed",
  "amountOut": "2412345678"
}

ETH Swap Flow (Direct)

For swapping ETH directly, send a POST to the ETH swap endpoint. This does not require Permit2 approval since you're sending native ETH.

curl Example

curl -X POST https://fastrpc.mev-commit.xyz/fastswap/eth \
  -H "Content-Type: application/json" \
  -d '{
    "sender": "0xYourAddress",
    "tokenOut": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
    "amountIn": "1000000000000000000",
    "minAmountOut": "2400000000",
    "fee": 500,
    "deadline": "1709500300",
    "signature": "0x YOUR_SIGNATURE"
  }'

Response:

{
  "txHash": "0x...",
  "status": "preconfirmed",
  "amountOut": "2412345678"
}

Common Token Addresses

Token	Address	Decimals
WETH	0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2	18
USDC	0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48	6
USDT	0xdAC17F958D2ee523a2206206994597C13D831ec7	6
DAI	0x6B175474E89094C44Da98b954EedeAC495271d0F	18
WBTC	0x2260FAC5E5542a773Aa44fBCfeDf7C193bc2C599	8

Uniswap V3 Fee Tiers

Fee	Description	Use Case
100	0.01%	Stablecoin pairs (USDC/USDT)
500	0.05%	Major pairs (ETH/USDC, ETH/USDT)
3000	0.3%	Standard pairs
10000	1%	Exotic pairs

Key Details

• Network: Ethereum mainnet (chain ID 1)
• ERC-20 swaps: Gasless for the user, relayer pays gas
• ETH swaps: Direct execution through FAST RPC
• Settlement: All swaps route through Uniswap V3 pools
• Preconfirmation: All swaps benefit from mev-commit builder commitments
• Slippage: Set minAmountOut to protect against price movement
• Deadline: Always set a deadline to prevent stale intents from executing