4️⃣Build Swap Transaction

When building transaction, there are 6 additional parameters along with quote input.

Field nameRequirement




Required when srcSwapDescription is presented in quote result


Required when dstSwapDescription is presented in quote result


Required when bridgeDescription is presented in quote result


Required when bridgeDescription is presented in quote result


Required when bridgeDescription is presented in quote result

To build transaction, please fill the corresponding fields (srcSwapDescription, bridgeDescription and dstSwapDescription) from quote response's route to buildTx input . If parameters are not filled properly, it may not return the desired routing result. You can review the transaction calldata route by checking route field in buildTx response.

For example, following response is quote result of Arbitrum USDT to KCC native token.

// quote response
    "success": true,
    "routes": [
            "srcChainId": 42161,
            "srcQuoteTokenAddress": "0xFd086bC7CD5C481DCC9C85ebE478A1C0b69FCbb9",
            "srcQuoteTokenAmount": "10000000",
            "dstChainId": 321,
            "dstQuoteTokenAddress": "0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE",
            "srcSwapDescription": null,
            "bridgeDescription": {
                "provider": "yBridge",
                // ...
            "dstSwapDescription": {
                "provider": "XY DexAggregator",
                // ...
            // ...
  • srcSwapDescription is null because these is no source chain swap needed in this route, so we don't have to fill srcSwapProvider when calling buildTx.

  • We have a non-empty bridgeDescription because it's a cross-chain quote. We need to fill corresponding bridgeProvider, srcBridgeTokenAddress and dstBridgeTokenAddress when calling buildTx. For single chain quote, we can skip these parameters.

  • dstSwapDescription is needed in this route. So we need to fill dstSwapProvider when calling buildTx.

Therefore, we can create the following buildTx request from above information:

// buildTx request
curl -G \
  -d 'srcChainId=42161' \
  -d 'srcQuoteTokenAddress=0xFd086bC7CD5C481DCC9C85ebE478A1C0b69FCbb9' \
  -d 'srcQuoteTokenAmount=10000000' \
  -d 'dstChainId=321' \
  -d 'dstQuoteTokenAddress=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE' \
  -d 'slippage=1' \
  -d 'bridgeProvider=yBridge' \
  -d 'srcBridgeTokenAddress=0xFd086bC7CD5C481DCC9C85ebE478A1C0b69FCbb9' \
  -d 'dstBridgeTokenAddress=0x0039f574eE5cC39bdD162E9A88e3EB1f111bAF48' \
  -d 'dstSwapProvider=XY%20DexAggregator' \

Parameter/Response Details

  • If you would like to know more about commissionRate fields and fee collection function, please refer to Monetization / Take Fees

  • If you would like to know latest supported bridge provider and swap provider, please refer to Supported Blockchains/Bridges/DEXs

  • The estimatedGas field in the API response is an estimated value. For now, please use a method similar to RPC, such as eth_estimateGas, to re-estimate the actual gas limit. You can refer to the following sample code to do that:

from web3 import Web3
import requests

if __name__ == "__main__":
    # 1st: get tx data from xy aggregator api
    endpoint = 'https://aggregator-api.xy.finance/v1/buildTx?srcChainId=137&srcQuoteTokenAddress=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&srcQuoteTokenAmount=9000000000000000000&dstChainId=56&dstQuoteTokenAddress=0x8AC76a51cc950d9822D68b83fE1Ad97B32Cd580d&slippage=1&receiver=0x9cEEEbdF49cF5DEa891C9D74f8ea03af2aCf284F&bridgeProvider=yBridge&srcBridgeTokenAddress=0x2791Bca1f2de4661ED88A30C99A7a9449Aa84174&dstBridgeTokenAddress=0x8AC76a51cc950d9822D68b83fE1Ad97B32Cd580d&srcSwapProvider=OneInch%20V4%20DexAggregator&affiliate=0x512E00f66217714BAee5F0736428b026e8c30AF5'
    resp = requests.get(endpoint)
    resp_json = resp.json()

    # 2nd: get estimateGas by calling web3 rpc
    rpc_endpoint = 'https://polygon.llamarpc.com'
    w3 = Web3(Web3.HTTPProvider(rpc_endpoint))
    estimate_gas = w3.eth.estimate_gas(resp_json["tx"])

    # 3rd: Combine the estimateGas with the tx data
    tx = resp_json["tx"]
    tx["gas"] = estimate_gas

    # 4th: sign the tx & send it
    priv_key = "0x"
    tx_signed = w3.eth.account.sign_transaction(tx, priv_key)
    tx_hash = w3.eth.send_raw_transaction(tx_signed.rawTransaction)

Example Request

$ curl https://aggregator-api.xy.finance/v1/buildTx?srcChainId=10&srcQuoteTokenAddress=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&srcQuoteTokenAmount=1000000000000000000&dstChainId=56&dstQuoteTokenAddress=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&slippage=1&receiver=0xb6EFA1C3679f1943f8aC4Fc9463Cc492435c6C92&bridgeProvider=yBridge&srcBridgeTokenAddress=0x94b008aA00579c1307B0EF2c499aD98a8ce58e58&dstBridgeTokenAddress=0x55d398326f99059fF775485246999027B3197955&affiliate=0x90d67a9eaC7324A1a2942D6Dea9f6174Ad6048c9&commissionRate=100000&srcSwapProvider=OKX+DEX&dstSwapProvider=OKX+DEX

This request is asking to bridge 1 ETH from Optimism for ETH on the BNB Chain

IMPORTANT: Note that the amount parameter should be padded with zeroes. For example, pass 100000000 instead of 100 if the decimals of the token is 6.

Here you can find our full API reference

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