Swap API Deep-Dive

The Swap API (/swap/approval) is the recommended integration path for most developers. It abstracts swap + bridge + swap into a single call and returns executable calldata.

Base URLs

• Mainnet: https://app.across.to/api
• Testnet: https://testnet.across.to/api

Integrator ID (required for production)

Before launch, register and obtain your 2-byte hex integrator ID (e.g., 0xdead). This ID is used for tracking and support.

Caching and Liveness

• Do not cache /swap/approval responses. Quotes are derived from on-chain state and can change every block.
• /deposit/status is the only stateful endpoint (indexer-backed). See deposit-tracking.md.

Trade Types

• exactInput: You specify the exact input amount. The API returns expected output after fees.
• minOutput: You specify the minimum output amount you will accept. The API computes required input.
• exactOutput: You specify the exact output amount required. If the API cannot deliver that exact amount, the transaction is cancelled and funds are refunded.

Slippage

• slippage=auto (default) lets the API choose an optimal value.
• A numeric slippage value must be between 0 and 1 — this is a ratio, not a percentage. 0.005 = 0.5%, 0.01 = 1%, 0.5 = 50%. A common mistake is passing 0.5 intending 0.5% — that would allow 50% slippage.
• Numeric slippage is split evenly across origin and destination swaps when both swaps exist.
• If only one swap happens (origin-only or destination-only), the full slippage is applied to that single leg.

GET /swap/approval

Returns data required to execute a crosschain swap. If the input token requires approval, approvalTxns is included.

Required query parameters

Optional query parameters

Response (key fields)

• crossSwapType: bridgeableToBridgeable, bridgeableToBridgeableIndirect, bridgeableToAny, anyToBridgeable, anyToAny
• approvalTxns[]: ERC-20 approvals to submit before the swap (chainId, to, data)
• checks: allowance and balance checks
• steps: originSwap, bridge, destinationSwap (present depending on route)
• fees: total, totalMax, and originGas breakdowns
• inputAmount, maxInputAmount, expectedOutputAmount, minOutputAmount
• expectedFillTime (seconds)
• swapTx: executable transaction data (chainId, to, data, gas, maxFeePerGas, maxPriorityFeePerGas, simulationSuccess)
• quoteExpiryTimestamp
• id (unique request identifier)

Errors

• 400: bad request due to invalid input
• 4XX: insufficient liquidity for same-asset bridging

POST /swap/approval (embedded actions)

Use this to build embedded crosschain actions that execute on the destination chain immediately after the swap.

• Query parameters are the same as GET, but the OpenAPI reference describes amount as the required output-token amount for POST. If you rely on exact-input semantics, verify behavior with the API before shipping.
• Request body includes an actions array.

Request body

{
  "actions": [
    {
      "target": "0x...",
      "functionSignature": "function transfer(address,uint256)",
      "args": [
        { "value": "0xRecipient", "populateDynamically": false },
        { "value": "0", "populateDynamically": true, "balanceSourceToken": "0xToken" }
      ],
      "value": "0",
      "isNativeTransfer": false
    }
  ]
}

Notes

• The OpenAPI spec for POST uses an upper-case crossSwapType enum (BRIDGEABLE_TO_BRIDGEABLE, BRIDGEABLE_TO_ANY, ANY_TO_BRIDGEABLE, ANY_TO_ANY).
• Treat the POST response as matching the GET response unless your integration depends on the specific enum casing.

End-to-End Example: Bridge USDC from Arbitrum to Base

This example shows the complete flow for a crosschain USDC transfer.

1. Get a quote

GET https://app.across.to/api/swap/approval?tradeType=exactInput&amount=10000000&inputToken=0xaf88d065e77c8cC2239327C5EDb3A432268e5831&outputToken=0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913&originChainId=42161&destinationChainId=8453&depositor=0xYourAddress&slippage=auto

• amount=10000000 = 10 USDC (6 decimals)
• inputToken = USDC on Arbitrum
• outputToken = USDC on Base

2. Check for approval transactions

If the response includes approvalTxns, submit each one and wait for confirmation before proceeding.

for (const approvalTx of response.approvalTxns) {
  const tx = await wallet.sendTransaction({
    to: approvalTx.to,
    data: approvalTx.data,
    chainId: approvalTx.chainId,
  });
  await tx.wait();
}

3. Submit the swap transaction

const swapTx = await wallet.sendTransaction({
  to: response.swapTx.to,
  data: response.swapTx.data,
  chainId: response.swapTx.chainId,
  gasLimit: response.swapTx.gas,
});
const receipt = await swapTx.wait();

4. Track the deposit

GET https://app.across.to/api/deposit/status?depositTxnRef={receipt.transactionHash}

Poll every 10 seconds until status = "filled".

Related endpoints

GET /swap/chains
GET /swap/tokens
GET /swap/sources
GET /swap/sources?chainId={id}

Use these to populate UIs and validate inputs before calling /swap/approval.