Answered from live records · 2026-09-15
What happens when Sato Swap simulates a transaction?
It runs the transaction against a node first: a route that reverts is withheld with the decoded reason, while a revert on your own missing approval is reported as a precondition instead, as of 2026-09-15.
The four simulation lanes and the three outcomes that get confused. A simulation is a reading at a block, not a promise about the next one: state moves, and a transaction that simulated cleanly can still revert when it lands.
| Lane or outcome | What it does |
|---|---|
| evm_rpc | Keyless. eth_call at latest state from the taker, then eth_estimateGas, each inside a bounded deadline. A revert is decoded where the venue returned a standard Error(string) or Panic(uint256) payload. |
| alchemy | alchemy_simulateExecution, only where a key is configured and the chain has a published host. It returns asset changes, so it yields a real expected output. Inert and unmentioned without the key. |
| solana_rpc | simulateTransaction over a public RPC against the venue's unsigned transaction. It returns logs and units consumed rather than an output amount, and the result says so instead of inventing one. |
| none | No lane could run, and the REASON is always given — “we did not check” and “we checked and it is clean” must never look alike. Under a policy that requires a simulation this is rule E7 and the transaction is withheld. |
| A revert in the route | Rule E4. The transaction is withheld and the decoded revert reason travels with the refusal. |
| A revert on YOUR allowance | Not a fault in the route. It is re-run against a state where the approval exists; where that is not possible, rule E9 returns the transaction with the precondition named — which approval, to which spender, for how much — and says plainly that the route itself was not simulated. Withholding on this would withhold every wallet's first swap, since a wallet cannot approve a router it was never handed. |
| The output amount | Not decoded on the keyless EVM lane. A router's return data is usually not a plain output amount, and printing “output not simulated” beats printing a number decoded by guessing at an ABI. |
How this was answered
simulateSwap() in lib/swap/simulate.ts and decideOnSimulation() in lib/swap/execute.ts: the four lanes, the two refusal rules (E4, E7) and the one precondition (E9) that is deliberately not a refusal.
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Sato Hub. "What happens when Sato Swap simulates a transaction?." Sato Hub, updated 2026-09-15, accessed 2026-09-16. https://satohub.ai/answers/what-happens-when-sato-swap-simulates-a-transactionData last refreshed 2026-09-15; this page is rebuilt daily. Citations carry the date so a reader can tell which snapshot a claim came from. Catalog data is licensed CC-BY-4.0 and the machine-readable copy is linked in the page's Dataset metadata.