Price impact

Price impact is the cost of your trade's own footprint. An AMM prices along a curve: as your swap removes one asset from the reserves and adds the other, the exchange rate shifts against you with every unit traded. The average rate you actually receive therefore sits below the marginal rate the pool displayed before you traded, and that difference is price impact.

The size of the effect is governed by one ratio: your trade amount versus the pool's reserves. Swapping an amount that is a tiny fraction of the reserves barely bends the curve; swapping a meaningful percentage of them bends it steeply. This is a structural property of constant-product pricing, not a fee anyone collects, and it exists even with zero other market participants.

Price impact is distinct from slippage, though the two are often conflated. Impact is deterministic and visible in your quote before you trade; slippage is the additional drift that occurs if reserves change between your quote and settlement. OneSwap's quote flow shows price impact for your exact amount before launch, and splitting a large order or choosing a deeper pool are the standard ways to reduce it.