The setting on a swap screen
On a decentralized exchange such as Uniswap you cannot fix the fill price, so you cap how far it may drift. Uniswap’s support center says its web app sets an automatic slippage of between 0.5% and 5%, depending on the network cost and the size of the swap, and lets you type a custom figure instead. Too low, and the swap may fail. Too high, and you may get fewer tokens than the preview showed.
Developers see the same limit as a minimum output. Uniswap’s developer guide sets that minimum to zero in its sample code and warns that doing so in production is “a significant risk”, because it exposes the trade to front-running and other price manipulation.
A worked illustration
The numbers here are round, not a live quote. Say a swap preview shows 1,000 USDC buying 500 units of a token, with tolerance at 0.5%. The lowest result the swap will accept is 497.5 units.
If the price moves and the pool would now return 498 units, the swap goes through and you receive two units fewer than the preview. If it would return 497, the swap fails instead. Raise the tolerance to 25% and the floor falls to 375 units; Uniswap’s own example says that at 25% “you may receive 25% fewer tokens” than the preview.
On an exchange order book
Centralized exchanges have slippage too. A market order fills against the best offers on the book, and a large one keeps eating into worse prices until it is complete, paying the taker fee on top.
Exchange Kraken shows a “fat finger” warning on Kraken Pro when the average slippage on an order would reach 3% or more, measured from the best available price to the projected fill price, and you must type CONFIRM to send it. Its support article, last updated August 8, 2025, says the warning covers spot trading only and has no API support.
Slippage is not price impact
Swap screens show two numbers that people mix up. Uniswap’s explainer says price impact is the change in price caused by your own trade against the pool, while slippage is the difference between what you expected and what you received once the swap was done.
A big order in a thin pool has a high price impact even if nobody else trades. Raising the tolerance does not shrink that cost. It only lets a worse fill through.
Before you confirm, open the swap details and compare both figures, and ask why a token would need a tolerance well above the automatic range.