Exact out

The goal of using "Exact Out" is to use "outAmount" to get desired "inAmount" on the frontend and receive the exact outAmount needed.

In the following, it will use OpenOcean’s reverseQuote API to calculate the required inAmount based on a target outAmount, then construct a swap transaction to complete an on-chain swap.

1. Obtain reverseQuote

✅ Description

Call the reverseQuote API to return the actual input token amount required based on the desired output token and amount. Please refer it here to get more info.

📍 Endpoint

GET https://open-api.openocean.finance/v4/eth/reverseQuote

📥 Parameters description：

Params	Description
inTokenAddress	Address of the input token (token to be swapped into on the frontend, same as outTokenAddress in /swap endpoint)
outTokenAddress	Address of the output token (token the user wants to receive, same as inTokenAddress in /swap endpoint)
amountDecimals	Amount of output token with decimals (e.g., 10 USDT should be written as 10000000)
gasPriceDecimals	gas price with decimals (obtain via /gasPrice here）
slippage	Set acceptable slippage by inputting a percentage value within the range of 0.05 to 50. e.g. input "1" refer to "1%" The default value of slippage is 1 (1%)

Example:

GET https://open-api.openocean.finance/v4/eth/reverseQuote?inTokenAddress=0xdac17f958d2ee523a2206206994597c13d831ec7&outTokenAddress=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&amountDecimals=10000000&gasPriceDecimals=5000000000&slippage=3

Response snippet:

{
  "code": 200,
  "data": {
    "inAmount": "10000000",
    "outAmount": "3869897038672758",
    "reverseAmount": 4075971843471952,
    ...
  }
}

Response params description:

Params	Description
inAmount	Desired output token amount (equal to the input parameter amountDecimals)
outAmount	Estimated output amount (for reference only)
reverseAmount	Actual amount of input tokens required (used as amountDecimals in /swap endpoint)

2. Call /swap endpoint to complete swaps

✅ Description

Use the response from reverseQuote endpoint to call the /swap endpoint, generate the transaction data, and complete the on-chain trade.

📍Endpoint

GET https://open-api.openocean.finance/v4/1/swap

📥 Parameters description:

Params	Description
inTokenAddress	Address of the input token (The outTokenAddress from reverseQuote )
outTokenAddress	Address of the output token (The inTokenAddress from reverseQuote )
account	Receiving address (can be a third-party address)
sender	Address used to initiate the transaction (user address)
amountDecimals	Input amount (The reverseAmount from reverseQuote )
gasPriceDecimals	gas price with decimals (obtain via /gasPrice here)
slippage	Set acceptable slippage by inputting a percentage value within the range of 0.05 to 50. e.g. input "1" refer to "1%" The default value of slippage is 1 (1%)
outAmountDecimals	Target exact-out output amount (The inAmountfrom reverseQuote )

Example:

GET https://open-api.openocean.finance/v4/1/swap?inTokenAddress=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&outTokenAddress=0xdac17f958d2ee523a2206206994597c13d831ec7&account=0x7899a562e9B0116bA8242ab8ae8bF01e3A00E43D&sender=0x7899a562e9B0116bA8242ab8ae8bF01e3A00E43D&amountDecimals=4075971843471952&gasPriceDecimals=5000000000&slippage=3&outAmountDecimals=10000000

Response snippet:

{
  "code": 200,
  "data": {
    "inAmount": "4075971843471952",
    "outAmount": "10000000",
    "value": "4075971843471952",
    "data": "...", // Can be used directly for on-chain execution
    ...
  }
}

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✅Whole Flow Overview

1. Call reverseQuote with the target outAmount to calculate the required inAmount;

2. Use reverseAmount and inAmount to construct the swap endpoint request;

3. Call swap, retrieve the transaction data, and execute the on-chain trade.

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🛠️Tips

• You can obtain the latest gasPriceDecimals from:

  GET https://open-api.openocean.finance/v4/:chain/gasPrice

• Use the price_impact from the reverseQuote response to evaluate the output price quote if reasonable, such as set a threshold of price impact to avoid large losses;

• All amount fields must be adjusted based on the token’s decimals (e.g., USDT uses 6, ETH uses 18).

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Reach out us in API support group if you'd like help wrapping this into a script (Python, JS, etc.) or building a front-end widget.