A route simulation is a rehearsal that can catch likely transaction failures. It checks whether a planned series of swaps and transfers appears to work with current blockchain data, before you approve the real transaction.
It runs the proposed transaction against a recent view of the blockchain, without making the real transfer. On many EVM networks, a service can use eth_call, a read-only request that asks contracts to run their checks without recording a transaction.
Suppose you want to move a token from one chain and receive another token on Solana. A route might swap your token, send value across a bridge, then swap again on the destination. Simulation checks the planned calls and expected outcomes as far as the available tools and data allow.
Each step has conditions. A swap may require enough token balance and permission to spend it; a bridge may need a valid amount and destination address. If a check fails during the rehearsal, the route is likely to fail when submitted too.
It can reveal failures that are already visible in the route’s inputs or current chain state. Examples include insufficient funds for the source transaction, a missing token approval, a contract rejecting the chosen amount, or a swap expected to return less than its minimum allowed output.
That last limit is often called slippage: the price can move between the quote and execution. If a route expects 100 tokens but allows at least 98, a simulation may show that the current estimate falls below 98. The transaction should then fail safely if that minimum is enforced, though a failed on-chain transaction can still consume network fees.
On Solana, the comparable dry run is called simulateTransaction. It can report program errors and resource use for a proposed transaction, but this still reflects a particular moment and setup.
A simulation is a forecast from a snapshot, not a promise about the future. If another trade changes a pool price, a block fills, or the route’s quote expires before your transaction is included, the real result can differ.
Some cross-chain routes also depend on a later transaction on another network. The source-chain transfer might succeed while a destination swap fails because the destination state changed or an expected condition no longer holds. The exact checks depend on the route and bridge design.
This is the trade-off: stricter minimum outputs can protect the amount you receive, but they also make a route more likely to fail after a small price move. A wider tolerance may allow completion with a worse result, so compare the minimum you would accept with the amount shown in the route.
Start with a small, clear example: choose the token and destination you want, then inspect the route’s steps, expected output, and minimum output. If the simulation reports an error, read which step failed and check that your wallet holds the needed asset and can cover the source network’s transaction fee.
Rango Bridge is a cross-chain routing service for finding ways to move or swap tokens between networks. For the broader explanation of how Rango Bridge chooses routes, see the route-selection guide; here, the useful point is to judge whether the selected plan can execute.
Before approving, make sure the simulated route still matches the action in your wallet: same source asset, destination, amount, and recipient. A changed amount or a newly quoted route may need a fresh check. Simulation reduces avoidable surprises, but it does not remove the need to review the transaction you are signing.