Every transaction broadcasts to the network before it confirms. Sits in a public waiting room called the mempool for a moment. Anyone watching can see what's coming.

Bot notices a large buy pending. Knows that buy will push the price up when it executes. Jumps ahead with a higher priority fee. Buys at current price. Original transaction confirms and pushes price higher. Bot sells into the move.

Milliseconds. Fully automated. No human making decisions. Just code running faster than anyone can react to.

Sandwich Attacks

The version that hits regular traders most often.

Bot spots the swap in the mempool. Calculates exactly how much price impact it'll cause based on order size relative to pool depth.

Buys the same token first. Price ticks up slightly. Original transaction executes at a worse price than the trader expected. Bot immediately sells everything back after. Pockets the gap.

Trader paid more than necessary. Bot collected the difference. Transaction was technically valid. Slippage tolerance was met. Nothing broken according to the rules. Just someone automated and faster extracting value from the trade.

High slippage tolerance is basically an open invitation. Set 10% tolerance, bot can extract up to 10% of the transaction value. Set 0.5% on a liquid pair and the sandwich becomes unprofitable. Not worth running.

MEV: The Bigger Picture

Front running is one piece of something called MEV. Maximal Extractable Value.

Validators ordering transactions don't have to process them in arrival order. They can reorder, insert, exclude within a block. Any value extractable through that ordering is MEV.

Sandwich attacks. Arbitrage between DEXs in a single block. Liquidation racing where bots compete to liquidate the same underwater position first. All of it.

Billions extracted annually on Ethereum. Entire research field built around it. Flashbots launched specifically to make MEV more transparent and less chaotic. Routing it through legitimate channels rather than gas wars where everyone overpays trying to front run each other.

Solana works differently. Jito validators enable MEV bundles. Priority fees matter more. Same fundamental dynamic underneath though. Sophisticated actors extracting value from regular traders through transaction ordering advantages that regular people don't have access to.

Why Nobody Gets Arrested For This

Traditional finance front running is illegal. Broker sees a client's large order. Buys ahead of it for their own account. Securities fraud. Breach of fiduciary duty. Prison.

Crypto mempool is public. No breach of trust. No privileged information. Just reading publicly available data faster than everyone else. Bot using the mempool is using information anyone could theoretically access.

Legally gray. Clearly harmful. Not clearly prosecutable under most existing frameworks. Some jurisdictions starting to look harder at it. No significant enforcement action yet.

How to Reduce Exposure

Private RPC endpoints are the main defense. Route transactions directly to validators instead of broadcasting to the public mempool. Front running bots can't see what they can't read.

Flashbots Protect on Ethereum. Transactions go through Flashbots relay instead of public mempool. Never visible before confirmation.

Jito on Solana does something similar. Private submission reducing mempool exposure significantly.

Not perfect. Doesn't eliminate all MEV. Dramatically reduces sandwich attack risk on anything meaningful.

Low slippage tolerance helps too. Makes sandwiching less profitable. Sometimes causes trades to fail in volatile conditions. Tradeoff worth understanding before adjusting settings.