3Route

https://api.3route.io/v1/pro/:chainId/swap

Build an unsigned swap transaction for the best route. Compare it with a fresh quote, validate every returned transaction field, obtain signing approval, and broadcast it through the chain's RPC. The parameters permit and usePermit2 are ignored. An ERC-20 source must approve the router in tx.to for at least srcAmount first. Supports exact-output amounts, historical state for approximately 35 days, and multiple amounts at once; the first request for a block may take 1-7 seconds.