Glossary
Front-Running
Submitting a transaction with a higher fee to be ordered ahead of a known pending transaction, profiting from advance knowledge of its effect.
Front-running is older than crypto — exchanges have policed it for decades — but it is endemic on public mempools where every pending transaction is visible. If a searcher sees a pending DEX trade that will move a price, they can submit their own trade at a higher fee to land first.
Most front-running on Ethereum is automated and runs through specialized bots. Defenses include private order flow (Flashbots, MEV Blocker), commit-reveal schemes, and order types that hide the swap until execution (CoW Protocol).