Why Most Crypto Bots Get Sandwiched (And How to Prevent It)

If you’ve ever tried building or running a crypto trading bot, you’ve probably encountered the dreaded sandwich attack. It’s one of the most frustrating and costly issues in decentralized finance (DeFi). I’ve spent months researching and experimenting with strategies to mitigate this problem, and in this article, I’ll explain exactly why sandwich attacks happen, how they work, and what you can do to protect your bot.

What Are Sandwich Attacks?

Sandwich attacks are a type of Maximal Extractable Value (MEV) attack where a malicious actor exploits the order of transactions in a block to profit at your expense. Here’s how it works:

1. Spotting Your Transaction: A bot monitors the mempool (the pool of pending transactions) for trades that will significantly impact the price of an asset, such as a large swap on a decentralized exchange (DEX) like Uniswap.
2. Front-Running: The attacker submits a transaction with a higher gas fee to execute before yours. They buy the asset you’re about to buy, driving up the price.
3. Back-Running: The attacker then submits another transaction to sell the asset immediately after your trade, profiting from the price difference you created.

The result? You pay more for the asset than you should, and the attacker pockets the difference.

Real-World Example

Let’s say you’re running a bot to swap 10 ETH for USDC on Uniswap. Here’s what happens:

• Your bot submits a transaction to swap 10 ETH for USDC.
• An attacker spots your transaction in the mempool.
• The attacker front-runs your transaction by buying 5 ETH, increasing the price of ETH.
• Your transaction executes at the higher price.
• The attacker back-runs your transaction by selling their 5 ETH, profiting from the price difference.

In this scenario, your bot loses value, and the attacker gains. It’s a zero-sum game—you’re the one who loses.

Why Are Sandwich Attacks So Common?

Sandwich attacks are prevalent for two main reasons:

1. MEV Bots Are Everywhere: MEV bots dominate Ethereum’s mempool, constantly scanning for profitable opportunities. If your transaction is visible in the mempool, it’s a target.
2. High Liquidity and Volume: Popular DEXs like Uniswap and SushiSwap attract millions of dollars in trading volume daily, making them lucrative hunting grounds for attackers.

According to Flashbots, MEV bots extracted over $1.2 billion in value from Ethereum users in 2022 alone. Sandwich attacks account for a significant portion of this.

How to Prevent Sandwich Attacks

After countless hours of trial and error, I’ve found a few effective strategies to mitigate sandwich attacks. Here’s what works:

1. Use Private Transactions (Jito Bundles)

One of the most effective ways to avoid sandwich attacks is to hide your transactions from the mempool using Jito bundles. Jito bundles are a feature of the Solana ecosystem that allows you to submit transactions directly to validators without exposing them to the public mempool.

Here’s how to implement Jito bundles:

from solana.rpc.api import Client
from solana.transaction import Transaction
from solana.publickey import PublicKey

# Initialize Solana client
client = Client("https://api.mainnet-beta.solana.com")

# Create a transaction
tx = Transaction()
tx.add_instruction(...)  # Add your swap instruction here

# Send the transaction as a Jito bundle
client.send_transaction(tx, {"skipPreflight": True, "maxRetries": 3})

By using Jito bundles, you bypass the mempool entirely, making it nearly impossible for MEV bots to spot and sandwich your transaction.

2. Split Large Trades into Smaller Batches

Another effective strategy is to split large trades into smaller batches. Instead of swapping 10 ETH at once, split it into ten transactions of 1 ETH each. This reduces the price impact of each trade, making it less profitable for attackers.

Here’s how to implement batching:

def batch_swap(amount, batch_size):
    batches = amount // batch_size
    remainder = amount % batch_size

    for _ in range(batches):
        swap_token(batch_size)  # Replace with your swap function

    if remainder > 0:
        swap_token(remainder)

3. Use Flashbots on Ethereum

On Ethereum, Flashbots is a popular solution for mitigating MEV attacks. Flashbots allows you to submit transactions directly to miners, bypassing the public mempool.

Here’s how to use Flashbots:

from web3 import Web3
from flashbots import Flashbot

# Initialize Web3 and Flashbot
w3 = Web3(Web3.HTTPProvider("https://mainnet.infura.io/v3/YOUR_INFURA_KEY"))
flashbot = Flashbot(w3, "YOUR_FLASHBOTS_KEY")

# Create a transaction
tx = {
    "to": "0xYourContractAddress",
    "value": w3.toWei(1, "ether"),
    "gas": 21000,
    "gasPrice": w3.toWei(50, "gwei"),
    "nonce": w3.eth.getTransactionCount("0xYourAddress"),
}

# Send the transaction via Flashbots
flashbot.send_bundle([tx], target_block=w3.eth.blockNumber + 1)

4. Optimize Gas Fees

Sometimes, your bot gets sandwiched because it’s using too low a gas fee. By setting a competitive gas fee, you can reduce the chances of being front-run.

Use tools like ETH Gas Station to calculate the optimal gas fee:

import requests

def get_gas_price():
    response = requests.get("https://ethgasstation.info/api/ethgasAPI.json")
    data = response.json()
    return data["fastest"] / 10  # Convert to Gwei

Lessons Learned

Through my journey fighting sandwich attacks, I’ve learned a few key lessons:

1. Visibility Is Your Enemy: The more visible your transactions are in the mempool, the more likely you are to be targeted.
2. Speed Matters: Faster transaction execution reduces the window of opportunity for attackers.
3. Adaptability Is Crucial: MEV bots are constantly evolving, so your strategies must evolve too.

Conclusion

Sandwich attacks are a major challenge for crypto trading bots, but they’re not insurmountable. By using tools like Jito bundles, Flashbots, and batching strategies, you can significantly reduce your risk of being exploited. The key is to stay informed, adapt to new threats, and continuously optimize your bot’s execution.

If you’re serious about building a profitable crypto bot, don’t let sandwich attacks derail your efforts. Implement these strategies, and you’ll be well on your way to success in the competitive world of DeFi.

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