Sandwich attack

A sandwich attack is when a trader spots your pending swap in the queue, places an order right before it and another right after, and pockets the price difference your trade creates. It matters because it quietly taxes ordinary swaps on decentralized exchanges, especially larger trades or ones with loose slippage settings, so what looks like a fair market price often includes a hidden cut for the attacker. For example, if you try to swap 5 ETH for a token with 3% slippage allowed, a bot can buy that token first, let your trade push the price up further, then sell into your purchase, profiting from the spread while you get a worse rate than quoted. Tighter slippage limits and private transaction routes like Flashbots Protect reduce the risk.