{
  "id": 16988889,
  "title": "A preflight for on-chain swaps: four rehearsals, three refusals, zero transactions",
  "url": "https://urgent.news/2026/10/29/a-preflight-for-on-chain-swaps-four-rehearsals-three-refusals-zero",
  "topic": "tech",
  "section": "Tech",
  "published": "2026-10-29T01:49:28.000Z",
  "source": {
    "name": "Dev.to",
    "slug": "dev-to",
    "url": "https://dev.to/blazephoenix_0bfac717a952/a-preflight-for-on-chain-swaps-four-rehearsals-three-refusals-zero-transactions-1n42"
  },
  "original_language": "en",
  "account": "On-chain swaps often fail during execution, wasting considerable gas in the process. A preflight check for these swaps using the BlazePhoenix SDK can prevent such failures without incurring any gas costs. In a simulated environment, the SDK can execute a function call to determine the outcome of a swap transaction, including the return value or a revert. This preflight step can be integrated into the signing process of wallets to catch errors early.\n\nThe SDK's simulate() method is used to create a plan for swapping tokens, such as WETH for USDC, with specific parameters like the amount and recipient. The plan is then executed to reveal any issues before any actual gas is spent. In the first layer, the simulation reveals that the swap fails due to the Router contract not being approved for the tokenIn, requiring an additional approval transaction. The simulate() method provides a clear error message stating the issue, making it easy to identify and resolve.\n\nFor scenarios where the wallet is not funded, a rehearsal can be conducted by overriding the state to include fake balances and allowances. This allows the preflight check to simulate the swap without actually spending any gas. By using a public client to call the contract with a stateOverride, the balance and allowance for WETH can be set, enabling the simulate() method to test the swap step in a controlled environment. This approach ensures that any potential issues are caught before the actual transaction is broadcast to the blockchain.",
  "summary": "Many swaps that fail on-chain, and burn gas doing it, would have shown the same failure in a free eth_call first. Here is a ~30-line preflight for swaps built with the BlazePhoenix SDK, run through four situations. Three get refused. None of them cost a wei. The idea A swap transaction is a function call. A node can execute any function call against current state without mining it, and tell you…",
  "key_points": [
    "Pre-flight check prevents on-chain swap failures with zero gas cost",
    "BlazePhoenix SDK simulates swap transactions to reveal issues",
    "State override enables rehearsal of swaps without gas expenditure"
  ],
  "editors_take": "Integrating simulated preflight checks into the wallet signing process shifts error detection from costly on-chain failures to free off-chain rehearsals, protecting users from wasting gas on unsuccessful transactions.",
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}