Use the Smart Order Router

The Smart Order Router (SOR) is a library for order routing optimization across Balancer pools for best price execution. It is a component of the SDK but also exists as a standalone package for integrators who only need swap routing logic. The example code and reference shown in the docs will use the SDK swaps module, but it should be straightforward to infer the changes required for the standalone SOR package.

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Note that you can also call the SOR through the Balancer API. Instructions on how to do this can be found here.

The below docs assume the SDK is installed and initialized:

import { BalancerSDK } from '@balancer-labs/sdk'

const balancer = new BalancerSDK({
  network: 1, // Mainnet
  rpcUrl: '' // rpc endpoint

const { swaps } = balancer // Swaps module

Swaps module abstracts the SOR and the general flow for finding a swap route includes the following steps:

Step 1. Pool data fetching

The SOR requires information about the available pools and their current status, including the prices of tokens and the liquidity of the pools. It is essential to use the SOR based on up-to-date information, as outdated information can lead to incorrect slippage predictions and potentially result in failed swaps.

await swaps.fetchPools()

Function is fetching pool data from subgraph and updates it with onchain balances then caches them internally.

Step 2. Route proposal

The SOR determines the optimal swap route based on the available pool data and the desired swap, taking into account factors such as swap size, gas costs, and slippage. When searching for swaps, developers have to choose between two types of swaps:

  • findRouteGivenIn, where the amount of tokens being sent to the pool is known, or
  • findRouteGivenOut, where the amount of tokens received from the pool is known.
const swapInfo = await swaps.findRouteGivenIn({
  tokenIn: '0xstring',          // address of tokenIn
  tokenOut: '0xstring',         // address of tokenOut
  amount: parseEther('1'),      // BigNumber with a swap amount
  gasPrice: parseFixed('1', 9), // BigNumber current gas price
  maxPools,                     // number of pool included in path, above 4 is usually a high gas price

The SOR returns the swap information, including the optimal swap route, the expected slippage and gas cost, and the estimated swap outcome as swapInfo.

  tokenAddresses: string[]      // tokens used in swaps
  swaps: SwapV2[]               // swaps calldata
  swapAmount: BigNumber
  swapAmountForSwaps: BigNumber // used for wrapped assets, eg: stETH / wstETH
  returnAmount: BigNumber
  returnAmountFromSwaps: BigNumber // used for wrapped assets, eg: stETH/wstETH
  returnAmountConsideringFees: BigNumber
  tokenIn: string
  tokenInForSwaps: string // Used with stETH/wstETH
  tokenOut: string
  tokenOutFromSwaps: string // Used with stETH/wstETH
  marketSp: string
Example response for ETH to wBTC swap
  tokenAddresses: [
  swaps: [
      poolId: '0xa6f548df93de924d73be7d25dc02554c6bd66db500020000000000000000000e',
      assetInIndex: 0,
      assetOutIndex: 1,
      amount: '1000000000000000000',
      userData: '0x',
      returnAmount: '7677860'
  swapAmount: BigNumber { _hex: '0x0de0b6b3a7640000', _isBigNumber: true },
  swapAmountForSwaps: BigNumber { _hex: '0x0de0b6b3a7640000', _isBigNumber: true },
  returnAmount: BigNumber { _hex: '0x7527a4', _isBigNumber: true },
  returnAmountFromSwaps: BigNumber { _hex: '0x7527a4', _isBigNumber: true },
  returnAmountConsideringFees: BigNumber { _hex: '0x752543', _isBigNumber: true },
  tokenIn: '0x0000000000000000000000000000000000000000',
  tokenInForSwaps: '0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2',
  tokenOut: '0x2260fac5e5542a773aa44fbcfedf7c193bc2c599',
  tokenOutFromSwaps: '0x2260fac5e5542a773aa44fbcfedf7c193bc2c599'
  marketSp: '13.022594322651878',

TODO: describe useBpts case

Step 3. Transaction encoding

To execute the swap, the returned swapInfo must be encoded into a transaction, which requires the following information:

const tx = swaps.buildSwap({
  userAddress: '0xstring',    // user address
  swapInfo,                   // result from the previous step
  kind: SwapType.SwapExactIn, // or SwapExactOut
  deadline,                   // BigNumber block timestamp
  maxSlippage,                // [bps], eg: 1 == 0.01%, 100 == 1%

Step 4. Broadcast transaction

const signer = balancer.provider.getSigner()
await signer.sendTransaction({
  value: tx.value