Backrun
Transaction primitives
A backrun is a transaction that executes immediately after another transaction in the same block to take advantage of the state that transaction leaves behind. The usual example is arbitrage: a large swap moves a pool’s price, and the backrunning transaction trades the gap it opened. A backrun does not change the order or the result of the transaction it follows.
Detailed explanation
A swap changes a pool’s price. If that leaves the pool out of line with the same token on another venue, there is a gap that a second transaction can close for a profit. Doing it right after the swap, before anyone else, is a backrun.
It differs from the strategies that act before a transaction. A backrun runs after its target and does not worsen the target’s execution, because the target has already filled when the backrun starts. The first trader’s price is the same with or without it.
Solana has no public mempool, so a searcher usually cannot see a transaction before it lands. In practice most backruns react to state that a validator has already processed, and the searcher races to land its own transaction in the next block. That is why the speed of the data feed and the reliability of the send path matter so much.
Searchers often submit the backrun as a Jito bundle so its legs execute atomically and carry a tip. The profit, if any, has to cover the pool fees, the priority fee and the tip, and many searchers compete for the same gap. No backrun strategy is guaranteed to pay.
When you'll see this
You see the term in MEV discussions, in searcher bots that watch large swaps on Raydium, Orca and Meteora pools, and in bundle transactions that land right after a big trade.
How NoLimitNodes uses this
Our Yellowstone gRPC feed delivers pool state as the validator processes it, which is what a backrun strategy reads. The MEV bots we build include a backrun arbitrage module, and we make no claim about its returns.
Related terms
- Jito Bundle · Up to five transactions a Jito block engine executes in order and atomically, with a tip that sets how it ranks.
- Atomic Transaction · A transaction that completes in full or has no effect. If one instruction fails, every change is rolled back.
- Triangular Arbitrage · Three swaps through three tokens that end where they began, so a price gap anywhere on the cycle can pay.
- Slippage · The gap between the price you quoted and the price you actually got, set as a tolerance on every swap instruction.
- Processed, Confirmed, Finalized · The three Solana commitment levels, ordered from "this validator saw it" to "supermajority will not roll it back."