API Quick Start Guide
Integrate decentralized cross-chain swaps between arbitrary assets into any applications (web apps, wallets, dApps) in just a few lines of code
Cross-chain value transfer has been one of the cornerstones in the world of truly decentralized finance. Blockchains are secure but isolated networks that don't have access to real-world data as well as to the state of other chains. Moreover, users have to rely on third-party services and centralized solutions, which are likely to request sensitive information or be susceptible to censorship. Every time a user performs a transfer through centralized bridges, the person has to bear the risk of their funds either being stuck due to an imbalance of liquidity on one of the sides of the bridge or being frozen due to centralization.
deBridge is a secure interoperability layer for Web3 that solves the problem of decentralization and enables seamless cross-chain value transfers across different chains.
deSwap is a solution built on top of deBridge infrastructure that enables capital-efficient cross-chain swaps between arbitrary liquid assets. It provides users, protocols, and DAOs with the ability to perform atomic cross-chain conversion of assets at the best market rates. And thanks to an execution fee β€” a small amount of the intermediary token that incentivizes anyone to execute the transaction on the destination chain β€” end-users just need to sign a single transaction on the source chain, without the necessity to have native coins for claiming the transfer and paying gas on the destination chain themselves.
Under the hood, deSwap consists of the following layers:
  • the transport layer (on-chain) is represented by the battle-tested and audited deBridge protocol, which is responsible for cross-chain messaging;
  • the forwarding layer (on-chain) is represented by periphery smart contracts that are responsible for communicating with deBridge gate, DEXs and aggregators for on-chain swaps;
  • the application layer (off-chain) is a set of off-chain services, responsible for finding the best swap routes across different DEXs (the planner), estimating cross-chain swaps (the estimator), and packing them into transactions ready to be submitted to the blockchains.
But don't be scared! The underlying complexity of deSwap is wrapped within a simple and intuitive B2B solution β€” deSwap API, which allows you to start constructing your very own cross-chain swap transactions in a matter of minutes!
Find the API specifications at our Swagger available at https://deswap.debridge.finance/ along with examples and schemas.

Use case: Swap USDT on Ethereum to MATIC on Polygon

Let's consider a real-life example: a user, who has 50 USDT on Ethereum, would like to receive MATIC on Polygon.

Estimating a swap

First, let's estimate the swap by calling the /estimate endpoint:
https://deswap.debridge.finance/v1.0/estimation?srcChainId=1&srcChainTokenIn=0xdAC17F958D2ee523a2206206994597C13D831ec7&srcChainTokenInAmount=50000000&slippage=1&dstChainId=137&dstChainTokenOut=0x0000000000000000000000000000000000000000&executionFeeAmount=auto
This request contains at least the following parameters representing our initial case:
  • srcChainId specifies the Ethereum chain id (1) as the chain swap is being initiated
  • srcChainTokenIn specifies the USDT token address (0xdAC17F958D2ee523a2206206994597C13D831ec7)
  • srcChainTokenInAmount specifies the desired input amount: since USDT token contract uses 6 decimals (the number of digits that come after the decimal place when displaying token values on-screen), the simple math: 50 * 10^6 leads to 50000000 as the value representing 50 USDT tokens
  • dstChainId specified the Polygon network chain id (137) as the target (destination) chain
  • dstChainTokenOut specifies the address of the target token; since MATIC is not a typical ERC-20 token represented by a smart contract but rather a native coin (a one-of-a-kind token within each EVM chain), we use a null (or zero) address to distinguish it from other tokens.
The following mandatory parameters are important as well:
  • The slippage parameter defines a constraint that acts as a safeguard to protect from a possible price drop. By specifying 1 (means 1%) we allow a DEX to perform exchange only if the actual outcome is not less than 99% of the estimated outcome.
  • executionFeeAmount=auto asks the estimator to include (and subtract it from the outcome) a minimum execution fee sufficient to incentivize anyone to execute the transaction on the destination chain
Sending this request will give us enough data to understand the outcome and its reasons. Under the estimation.dstChainTokenOut we can see the actual amount of MATIC the user may receive as a result of the swap:
"estimation": {
"dstChainTokenOut": {
"address": "0x0000000000000000000000000000000000000000",
"name": "MATIC",
"symbol": "MATIC",
"decimals": 18,
"amount": "29570160331501581528",
"minAmount": "29274458728186565713"
},
}
This implies that the user is expected to receive 29.57 MATIC (29570160331501581528 / 10^18), and at least 29.27 MATIC in a worst-case scenario (which corresponds to 99% of the estimated value since the slippage was initially set to 1%).
Other than that, we can find the estimation.executionFee object containing details about the execution fee token and the amount which has been subtracted from the estimated outcome:
"estimation": {
"executionFee": {
"token": {
"address": "0x1dDcaa4Ed761428ae348BEfC6718BCb12e63bFaa",
"name": "deBridge USD Coin",
"symbol": "deUSDC",
"decimals": 6
},
"recommendedAmount": "89031",
"actualAmount": "89031"
}
}
This means that the planner has picked deUSDC token as the intermediary token (used to bridge liquidity across chains), and the deBridge gate will withhold 0.089031$ (nine cents!) of it as an incentive to anyone who is willing to execute the transaction on the destination chain. In other words, by giving the deBridge gate explicit permission to hold a small amount as an execution fee, you don't have to worry about claiming the final transaction on the Polygon chain (which implies that you need to have some MATIC token beforehand to do this!), the cross-chain swap will finish automatically on your behalf!

Getting a transaction

Okay, you've received an estimation, the expected execution fee and the outcome are satisfactory. Now it's time to get the transaction that initiates the desired cross-chain swap. There is the /transaction endpoint for that, which expects at least all the parameters the /estimation endpoint does, and additionally two wallet addresses on the destination chain:
  • dstChainTokenOutRecipient, the address target tokens should be transferred to after the swap, and
  • dstChainFallbackAddress, the address target or intermediary tokens should be transferred in case of a failed swap (e.g., a swap may fail due to slippage constraints).
Putting it all together, the following request may be made:
https://deswap.debridge.finance/v1.0/transaction?srcChainId=1&srcChainTokenIn=0xdAC17F958D2ee523a2206206994597C13D831ec7&srcChainTokenInAmount=50000000&slippage=1&dstChainId=137&dstChainTokenOut=0x0000000000000000000000000000000000000000&executionFeeAmount=auto&dstChainTokenOutRecipient=0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045&dstChainFallbackAddress=0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045
The result of this request contains two objects. The estimation object has the same name and structure as inside the result of the /estimation endpoint, you are already familiar with. It may contain values that are slightly different from the previous call, as the prices of crypto assets are highly volatile, so don't be surprised to see a corrected estimation.
The tx object has the following structure:
"tx": {
"to": "0x663DC15D3C1aC63ff12E45Ab68FeA3F0a883C251",
"data": "0x61b36437000000000000000000000000dac17f958d2ee523a2206206994597c13d[...]",
"value": "1000000000000000"
}
and represents the constructed transaction ready to be signed and sent to the blockchain!

Submitting a transaction

Field names from the tx object speak for themselves:
  • the to is the field the transaction should be sent to, and typically you should expect the address of one of the smart contracts responsible for forwarding;
  • the data is the contents of the transaction, containing instructions related to swaps planned on the source or (and) on the destination chains, bridging settings, etc;
  • the value is the amount of native coins that must be sent along with the transaction.
However, there are a few things you must consider:
First, the value is always positive, even if you plan to swap an ERC-20 token. This is because the underlying deBridge protocol takes a fixed amount in the base asset of the blockchain, and the API always includes it as the transaction value. In the above example, the value equals the current fixed fee, which is 0.001 ETH on the Ethereum blockchain. You can learn more about this by reading the deBridge protocol documentation. Soon we'll give everyone the ability to pay this fixed fee in the input asset rather than the native coin.
Second, in case you plan to swap an ERC-20 token, you need to give approval to the smart contract address specified in the tx.to field prior to submitting this transaction so it can transfer them on the behalf of the sender. This can be typically done by calling either approve() or increaseAllowance() method of the smart contract which implements the token you are willing to swap. Approve at least the amount of tokens you are going to swap.
Third, our smart contracts support EIP-2612-compliant signed approvals, so the necessity to give the approval (described above) can be eliminated by providing an approval signed off-chain by the sender.
Other than that, the transaction is ready to be signed by the sender and sent to the blockchain via your favorite RPC node.

Best practices

Don't forget to specify your invitation code as the referralCode parameter when calling the /transaction endpoint. If you don't have it, you can get one by pressing the WAGMI button at https://app.debridge.finance/. Governance may thank you later for being an early builder.
Don't delay the transaction: since cryptoassets are highly volatile, the prices may change drastically within a short period of time which may cause swaps to fail because of changed prices and outdated slippage constraints. We recommend submitting the transaction within two minutes after construction or refreshing it's data by calling the /transaction endpoint again.

Understanding the execution fee

The execution fee is a small amount of the intermediary token that incentivizes anyone to execute the transaction on the destination chain. In other words, the execution fee must cover the cost of gas needed to execute the transaction. To estimate the execution fee, the estimator estimates the amount of gas units the transaction is expected to consume, multiplies it by the current price per gas unit, and adds a 30% margin to make it profitable for a claimer.
This means that the execution fee dramatically differs across different chains: a few cents on the Polygon network, a few dollars on the BNB chain, $10-20 on the Arbitrum One chain, and more than $50 on the Ethereum chain.

Understanding the asset of the execution fee

The execution fee is a small amount of the intermediary token that incentivizes anyone to execute the transaction on the destination chain. It is important to understand that the intermediary token is a select token used to transfer liquidity between chains. In the example above, we saw the deUSDC token as an intermediary token baked 1:1 by USDC collateral on Ethereum, but there may be other tokens as well. For example, there is a deETH intermediary token on the Arbitrum One chain baked 1:1 by ETH collateral hold on Ethereum. We are working to provide more intermediary tokens and increase liquidity on popular DEXs.
This means that you must never have a fixed amount as the execution fee, since the values may be represented in various assets. For example, at the time of writing, there are two intermediary tokens on the Arbitrum blockchain, and the execution fees may look as follows:
  • 0.003653 deETH (β‰ˆ12.2$), if the planner picks deETH as the intermediary token,
  • 18.772567 deUSDC, if the planner picks deUSDC as the intermediary token.
It is also important to understand that the planner picks the best route by the maximum outcome (with execution fee subtracted), not by the lowest execution fee itself.

FAQ

What is the difference between the /estimation and the /transaction endpoints?

You might have noticed that the /transaction endpoint provides the complete estimation of the route, so you might wonder about the purpose of the separate /estimation endpoint. The reason is the performance and latency: doing numerous estimations in a row may be faster when calling /estimation as it does not use some heavyweight calls used by the /transaction endpoint.

Why can't I swap to/from token X?

We use data from the 1inch aggregator (more aggregators are on the way!) to find the best market rates across known DEXs. However, there may be tokens that are not listed on any DEX or miss adequate liquidity for their token. In any of these cases, we cannot provide you with a route for a swap.
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On this page
Use case: Swap USDT on Ethereum to MATIC on Polygon
Best practices
Understanding the execution fee
Understanding the asset of the execution fee
FAQ