Plain English
Front-running is when a bot sees your transaction in the mempool, predicts it will move the price, and submits its own version with a higher fee — getting executed first and capturing the price impact you would have benefited from. Especially common on DEX swaps for less-liquid tokens.
How it actually works
The attacker monitors the mempool. When a profitable target appears (large buy that will move price up), the bot submits a buy with higher priority fee, then waits for your trade to push price, then sells. You get a worse fill; the bot pockets the difference. This pattern accelerated as MEV-Boost gave searchers structured ways to compete for block inclusion.
What it means for you
Avoid the public mempool for sensitive trades. Flashbots Protect, MEV Blocker, and CoW Swap are the standard defenses. For institutional-size trades, OTC desks or dark pools bypass the mempool entirely. Never assume your DEX swap is private — it is the opposite of private until it confirms.
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Educational content only. Not investment, tax, or legal advice.