Definition
Fee sniping is a mining strategy in which a miner deliberately re-mines one or more of the most recent blocks to seize their transaction fees, instead of simply building on top of them. The attacker effectively orphans the previous block and reclaims both the fees it contained and any lucrative new transactions that have since arrived in the mempool.
The Economic Trigger
Re-mining a tip is statistically harder than extending the chain, so today it rarely pays off. But the calculus changes as the block subsidy shrinks through successive halvings. When fees dominate block revenue, a block stuffed with high-fee transactions becomes a tempting target. If the next block's available fees are much smaller than the fees sitting in the block just behind it, a miner may rationally gamble on a one-block reorganization to capture the richer reward.
How Wallets Defend
The standard countermeasure is anti-fee-sniping using nLockTime. Wallets such as Bitcoin Core and Electrum set each transaction's locktime to the current block height, meaning the transaction is only valid from the next block forward. A miner attempting to re-mine the past block cannot include these freshly broadcast transactions, so it quickly runs out of fee-paying material to steal, undermining the attack's profitability.
Fee sniping is closely tied to the broader incentive dynamics that determine whether miners ever attempt a chain reorganization. As subsidy continues to decline, fee-driven behavior of this kind is expected to receive more scrutiny. Related concepts include double-spending and the longest-chain rule.
In Simple Terms
Fee sniping is a mining strategy in which a miner deliberately re-mines one or more of the most recent blocks to seize their transaction fees,…