DeFi · 52 / 86 · 3 min
Swaps
An automated swap sells you one token for another from a pool, at a price that moves as you trade. The number you see and the number you get can differ.
The pool's price moves as you trade. The number you see and the number you get can differ.
A worked case
A person swaps a large amount against a small pool. The screen showed a price before they clicked. The fill is worse, and a fee sits on top. They blame the wallet. The pool did what a pool does: the price moved because they traded.
The price moves as you trade
A small pool moves a lot when you trade a large size. That movement is slippage. The app may show a minimum you will accept. If the market runs past it, the trade fails, and you may still pay gas.
Who gets paid
The pool's liquidity providers, the interface, and the chain. A free front end can still route you through a toll someone chose.
Compare the rate with a second interface you opened yourself before you sign a large swap.
The pool moved because you traded
Automated market makers, the design Uniswap published and then everyone copied, do not have an order book. A pool holds two tokens. The price is a formula. Your trade moves the formula. A small trade in a deep pool barely moves it. A large trade in a shallow pool pays a worse price than the screen showed a second earlier, and then pays a fee. That gap has a name, price impact, and it is not a bug in your wallet.
People meet this on a phone, accept a default slippage, and then blame the wallet when the fill is ugly or when someone else trades in front of them inside that slippage. The wallet did what you signed. The pool did what the formula says. If you cannot state the pool's size next to your trade's size, you do not know the price. You know a quote from before you existed in the pool.
Set a limit you would actually accept, or trade less. The interface is allowed to make the default wide, because a failed swap is a support ticket and a worse fill is quiet.
Read it yourself
These links are the record. They are not a recommendation, and they are not instructions. A news story or a court paper can still be wrong about a detail. The check does not change because a famous name is in the story.
Apply the check
Open a question. The line is about this topic. It is not a verdict that anything is safe.
The pool's fee, and whoever traded ahead of you.
The pool's formula. Your size decides how far it moves.
The worse fill, once you sign. Slippage settings are your limit, if you set them.
Check yourself
Is the quoted price guaranteed?
Only within the slippage limit you accept. Outside it, the trade should fail.
After this you can read the minimum you will receive before you sign a swap.