Set a Slippage Limit Before a Cross-Chain Swap

A cross-chain swap moves through markets on more than one blockchain, where prices and available liquidity can change while the transaction is underway. A slippage limit sets the worst price movement a swap leg may accept before it fails; it does not cap every cost or guarantee a destination-chain fill.

That distinction matters when a route swaps tokens before bridging, after bridging, or on both sides. For example, Across’s Swap API accepts an automatic setting or a numeric tolerance, and divides a numeric setting equally between origin and destination swap legs when both are used. For timing context, see Acrossbridge route-by-route transfer times; a transfer’s duration can affect how much a market moves before the route completes.

A limit that is too loose can accept a worse exchange rate, while one that is too tight can leave a transaction unfilled.

What does a slippage limit control?

It sets the minimum output the swap will accept relative to the quote, or the maximum price movement allowed before execution reverts. With an exact-input trade, you specify what you send and accept an output that may vary within the limit; with a minimum-output trade, you specify the least you are willing to receive.

The limit applies to swap execution, not necessarily the bridge’s fee, network gas, or the time it takes for assets to arrive. A quote can show an estimated output, but the amount you actually receive depends on the route’s rules and whether each swap leg executes within its bound.

Why can a cross-chain route need more room?

A route with two swaps can face price changes in two separate pools. Liquidity may be thinner for one leg, and the destination swap may happen after the origin transaction has already been submitted, so the two prices are not locked together by one atomic trade.

Some routes bridge a token without swapping on one or both chains. In those cases, there may be fewer swap legs exposed to slippage, but fees, confirmation delays, and the route’s completion conditions still affect the result. Check which assets and chains the quote covers, and whether the displayed tolerance applies per leg or across the route.

How should you choose a limit?

Start with the wallet or service’s quoted output and inspect the minimum output it will enforce. A wider tolerance gives execution more room when markets move, but also means accepting a less favorable exchange rate; a narrower one protects the price more tightly and raises the chance of a failed swap.

• Compare the quoted output with the minimum you would accept.
• Check whether the route includes origin and destination swaps.
• Review fees and gas separately from the slippage setting.
• For a large trade, consider splitting it if the quote shows limited liquidity.

Automatic tolerance can be a reasonable default when you do not know how to allocate limits across a multi-leg route, but inspect the quote before signing. If you set a numeric value, verify how the interface interprets it: some APIs expect a decimal fraction, so 0.005 represents 0.5%, not 0.005%.

Use the tightest limit that still gives the route a realistic chance to execute at the quoted market conditions. If the minimum output is unacceptable, refresh the quote or choose another route instead of widening the limit by habit.