Front-Running
Front-running is jumping ahead of someone's pending transaction for profit — seeing your big buy in the mempool, buying first, then selling into your price
Front-running is jumping ahead of someone’s pending transaction for profit — seeing your big buy in the mempool, buying first, then selling into your price impact. On-chain it’s usually bots, not people, and it’s the most common form of MEV extraction.
Why it matters
Front-running is why your swap sometimes executes worse than quoted: the difference is someone else’s profit. Defenses are practical — low slippage tolerance, private RPCs, and avoiding huge trades in thin pools — not theoretical. If you trade on DEXs, you operate in MEV territory every time.