Quickstart

This guide walks through creating and executing a token swap on CoW Protocol using the Python SDK, learning how to swap tokens with built-in MEV protection and gasless trading.

CoW Protocol employs batch auctions to protect traders from MEV and provides the best execution prices by aggregating liquidity across multiple DEXs.

Prerequisites

Before starting, ensure you have:

The CoW Protocol Python SDK installed
A wallet with test tokens (Sepolia testnet)
Your wallet’s private key
Approval for the CoW Protocol Vault Relayer to spend your tokens

You must approve the CoW Protocol Vault Relayer contract before executing a swap.

Environment Setup

Create a .env file in your project root:

PRIVATE_KEY=0x1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef

Add .env to .gitignore to prevent accidentally committing your private key.

Install the required package:

pip install python-dotenv

Complete Swap Example

import os
import asyncio
from dotenv import load_dotenv
from web3 import Account, Web3
from web3.types import Wei
from cowdao_cowpy.cow.swap import swap_tokens
from cowdao_cowpy.common.chains import Chain

BUY_TOKEN = Web3.to_checksum_address(
    "0xfFf9976782d46CC05630D1f6eBAb18b2324d6B14"
)  # WETH
SELL_TOKEN = Web3.to_checksum_address(
    "0xbe72E441BF55620febc26715db68d3494213D8Cb"
)  # USDC

SELL_AMOUNT_BEFORE_FEE = Wei(5000000000000000000)
CHAIN = Chain.SEPOLIA

load_dotenv()
PRIVATE_KEY = os.getenv("PRIVATE_KEY")

if not PRIVATE_KEY:
    raise ValueError("Missing PRIVATE_KEY in .env file")

ACCOUNT = Account.from_key(PRIVATE_KEY)

async def main():
    result = await swap_tokens(
        amount=SELL_AMOUNT_BEFORE_FEE,
        account=ACCOUNT,
        chain=CHAIN,
        sell_token=SELL_TOKEN,
        buy_token=BUY_TOKEN,
    )
    print(f"Order created successfully!")
    print(f"Order UID: {result.uid}")
    print(f"Order URL: {result.url}")

if __name__ == "__main__":
    asyncio.run(main())

Understanding the Code

Import Dependencies

from web3 import Account, Web3
from web3.types import Wei
from cowdao_cowpy.cow.swap import swap_tokens
from cowdao_cowpy.common.chains import Chain

The SDK uses web3.py for Ethereum interactions and provides a simple swap_tokens function.

Configure Token Addresses

BUY_TOKEN = Web3.to_checksum_address(
    "0xfFf9976782d46CC05630D1f6eBAb18b2324d6B14"
)  # WETH
SELL_TOKEN = Web3.to_checksum_address(
    "0xbe72E441BF55620febc26715db68d3494213D8Cb"
)  # USDC

Always use checksummed addresses to avoid errors via Web3.to_checksum_address().

Specify Sell Amount

SELL_AMOUNT_BEFORE_FEE = Wei(5000000000000000000)

Amounts are specified in the token’s smallest unit. Use Web3.to_wei() for easier conversion: Web3.to_wei(50, 'ether') equals 50 tokens with 18 decimals.

Select Network

CHAIN = Chain.SEPOLIA

Supported networks include: MAINNET, GNOSIS, SEPOLIA, ARBITRUM_ONE, BASE, POLYGON, AVALANCHE, and BNB.

Execute the Swap

result = await swap_tokens(
    amount=SELL_AMOUNT_BEFORE_FEE,
    account=ACCOUNT,
    chain=CHAIN,
    sell_token=SELL_TOKEN,
    buy_token=BUY_TOKEN,
)

The function handles quote retrieval, order creation and signing, orderbook submission, and returns the order UID and explorer URL.

Advanced Options

result = await swap_tokens(
    amount=SELL_AMOUNT_BEFORE_FEE,
    account=ACCOUNT,
    chain=CHAIN,
    sell_token=SELL_TOKEN,
    buy_token=BUY_TOKEN,
    slippage_tolerance=0.01,  # 1% slippage (default: 0.5%)
    partially_fillable=False,  # Allow partial fills (default: False)
    valid_to=None,  # Order expiry timestamp (default: uses quote expiry)
    env="prod"  # Environment: "prod", "staging", or "barn" (default: "prod")
)

Slippage Tolerance protects against price changes between order creation and execution. A 1% slippage means accepting up to 1% less than the quoted amount.

Working with Safe Wallets

To create orders from a Safe wallet:

from eth_typing.evm import ChecksumAddress

safe_address = Web3.to_checksum_address("0x...")

result = await swap_tokens(
    amount=SELL_AMOUNT_BEFORE_FEE,
    account=ACCOUNT,  # Signer account
    chain=CHAIN,
    sell_token=SELL_TOKEN,
    buy_token=BUY_TOKEN,
    safe_address=safe_address,  # Safe wallet address
)

When using a Safe wallet, the order uses pre-signature validation. The account parameter should be one of the Safe owners signing the transaction.

Fetching Order Information

After creating an order, fetch its details using the OrderBook API:

from cowdao_cowpy.order_book.api import OrderBookApi
from cowdao_cowpy.order_book.generated.model import UID

order_book_api = OrderBookApi()

order = await order_book_api.get_order_by_uid(
    UID("0x...your-order-uid...")
)

print(f"Order status: {order.status}")
print(f"Sell amount: {order.sellAmount}")
print(f"Buy amount: {order.buyAmount}")

Common Issues

Insufficient Token Balance

Ensure your wallet has enough of the sell token. Account for token decimals when checking balances.

Missing Token Approval

Before swapping, approve the CoW Protocol Vault Relayer:

from cowdao_cowpy.common.constants import CowContractAddress

vault_relayer = CowContractAddress.VAULT_RELAYER.value

Order Not Executing

Orders may take time to execute using batch auctions. Check the order status via the explorer URL returned by swap_tokens(). Orders expire if they don’t find a match within their validity period.

Next Steps

Explore Order Management to learn how to fetch, monitor, and cancel orders
Investigate Advanced Features for composable orders and TWAP strategies
Browse the API Reference for complete documentation
Learn about Contract Interaction with CoW Protocol smart contracts
Read the Testing Guide for how to test on Sepolia and graduate to production

Getting Started

Concepts

Guides

Advanced

API Reference

Prerequisites

Environment Setup

Complete Swap Example

Understanding the Code

Import Dependencies

Configure Token Addresses

Specify Sell Amount

Select Network

Execute the Swap

Advanced Options

Working with Safe Wallets

Fetching Order Information

Common Issues

Next Steps

​Prerequisites

​Environment Setup

​Complete Swap Example

​Understanding the Code

​Import Dependencies

​Configure Token Addresses

​Specify Sell Amount

​Select Network

​Execute the Swap

​Advanced Options

​Working with Safe Wallets

​Fetching Order Information

​Common Issues

​Next Steps

Prerequisites

Environment Setup

Complete Swap Example

Understanding the Code

Import Dependencies

Configure Token Addresses

Specify Sell Amount

Select Network

Execute the Swap

Advanced Options

Working with Safe Wallets

Fetching Order Information

Common Issues

Next Steps