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Getting a Quote

Introduction​

This guide will cover how to get the current quotes for any token pair on the Uniswap protocol. It is based on the Quoting code example, found in the Uniswap code examples repository. To run this example, check out the examples's README and follow the setup instructions.

info

If you need a briefer on the SDK and to learn more about how these guides connect to the examples repository, please visit our background page!

In this example we will use quoteExactInputSingle to get a quote for the pair USDC - WETH. The inputs are the token in, the token out, the amount in and the fee.

The fee input parameters represents the swap fee that distributed to all in range liquidity at the time of the swap. It is one of the identifiers of a Pool, the others being tokenIn and tokenOut.

The guide will cover:

  1. Computing the Pool's deployment address
  2. Referencing the Pool contract and fetching metadata
  3. Referencing the Quoter contract and getting a quote

At the end of the guide, we should be able to fetch a quote for the given input token pair and the input token amount with the press of a button on the web application.

For this guide, the following Uniswap packages are used:

The core code of this guide can be found in quote.ts

Example configuration​

We will use the example configuration CurrentConfig in most code snippets of this guide. It has the format:

import { Token } from '@uniswap/sdk-core'

interface ExampleConfig {
  rpc: {
    local: string
    mainnet: string
  }
  tokens: {
    in: Token
    amountIn: number
    out: Token
    poolFee: number
  }
}

export const CurrentConfig: ExampleConfig = {...}

The default config of the example uses a local fork of mainnet. If you haven't already, check out our local development guide. To change the rpc endpoint or the Pool used, edit the Currentconfig. To connect to mainnet directly, set the mainnet field in the config:

export const CurrentConfig: ExampleConfig = {
  rpc: {
    local: 'http://localhost:8545',
    mainnet: 'https://mainnet.infura.io/v3/0ac57a06f2994538829c14745750d721',
  },
  tokens: {
    in: USDC_TOKEN,
    amountIn: 1000,
    out: WETH_TOKEN,
    poolFee: FeeAmount.MEDIUM,
  },
}

The pool used is defined by a pair of tokens in constants.ts. You can also change these two tokens and the fee of the pool in the config, just make sure a Pool actually exists for your configuration. Check out the top pools on Uniswap info.

Computing the Pool's deployment address​

To interact with the USDC - WETH Pool contract, we first need to compute its deployment address. If you haven't worked directly with smart contracts yet, check out this guide from Alchemy. The SDK provides a utility method for that:

import { computePoolAddress } from '@uniswap/v3-sdk' 

const currentPoolAddress = computePoolAddress({
  factoryAddress: POOL_FACTORY_CONTRACT_ADDRESS,
  tokenA: CurrentConfig.tokens.in,
  tokenB: CurrentConfig.tokens.out,
  fee: CurrentConfig.tokens.poolFee,
})

Since each Uniswap V3 Pool is uniquely identified by 3 characteristics (token in, token out, fee), we use those in combination with the address of the PoolFactory contract to compute the address of the USDC - ETH Pool. These parameters have already been defined in our constants.ts file:

const WETH_TOKEN = new Token(
  1,
  '0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2',
  18,
  'WETH',
  'Wrapped Ether'
)

const USDC_TOKEN = new Token(
  1,
  '0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48',
  6,
  'USDC',
  'USD//C'
)

These constants are used in the config.ts file, as mentioned in the Introduction.

We can find the Pool Factory Contract address for our chain here.

Referencing the Pool contract and fetching metadata​

Now that we have the deployment address of the USDC - ETH Pool, we can construct an instance of an ethers Contract to interact with it:

import { ethers } from 'ethers'

const provider = new ethers.providers.JsonRpcProvider(rpcUrl)
const poolContract = new ethers.Contract(
  currentPoolAddress,
  IUniswapV3PoolABI.abi,
  provider
)

To construct the Contract we need to provide the address of the contract, its ABI and the provider that will carry out the RPC call for us. We get access to the contract's ABI through the @uniswap/v3-core package, which holds the core smart contracts of the Uniswap V3 protocol:

import IUniswapV3PoolABI from '@uniswap/v3-core/artifacts/contracts/interfaces/IUniswapV3Pool.sol/IUniswapV3Pool.json'

Having constructed our reference to the contract, we can now access its methods through our provider. We use a batch Promise call. This approach queries state data concurrently, rather than sequentially, to minimize the chance of fetching out of sync data that may be returned if sequential queries are executed over the span of two blocks:

const [token0, token1, fee, liquidity, slot0] = await Promise.all([
  poolContract.token0(),
  poolContract.token1(),
  poolContract.fee(),
  poolContract.liquidity(),
  poolContract.slot0(),
])

The return values of these methods will become inputs to the quote fetching function. The token0 and token1 variables are the addresses of the tokens in the Pool and should not be mistaken for Token objects from the sdk. For the full code, check out getPoolConstants() in quote.ts.

note

In this example, the metadata we fetch is already present in our inputs. This guide fetches this information first in order to show how to fetch any metadata, which will be expanded on in future guides.

Referencing the Quoter contract and getting a quote​

To get quotes for trades, Uniswap has deployed a Quoter Contract. We will use this contract to fetch the output amount we can expect for our trade, without actually executing the trade. Check out the full code for the following snippets in quote.ts

Like we did for the Pool contract, we need to construct an instance of an ethers Contract for our Quoter contract in order to interact with it:

const quoterContract = new ethers.Contract(
  QUOTER_CONTRACT_ADDRESS,
  Quoter.abi,
  getProvider()
)

We get access to the contract's ABI through the @uniswap/v3-periphery package, which holds the periphery smart contracts of the Uniswap V3 protocol:

import Quoter from '@uniswap/v3-periphery/artifacts/contracts/lens/Quoter.sol/Quoter.json'

We get the QUOTE_CONTRACT_ADDRESS for our chain from Github.

We can now use our Quoter contract to obtain the quote.

In an ideal world, the quoter functions would be view functions, which would make them very easy to query on-chain with minimal gas costs. However, the Uniswap V3 Quoter contracts rely on state-changing calls designed to be reverted to return the desired data. This means calling the quoter will be very expensive and should not be called on-chain.

To get around this difficulty, we can use the callStatic method provided by the ethers.js Contract instances. This is a useful method that submits a state-changing transaction to an Ethereum node, but asks the node to simulate the state change, rather than to execute it. Our script can then return the result of the simulated state change:

const quotedAmountOut = await quoterContract.callStatic.quoteExactInputSingle(
  token0,
  token1,
  fee,
  fromReadableAmount(
    CurrentConfig.tokens.amountIn,
    CurrentConfig.tokens.in.decimals
  ).toString(),
  0
)

The fromReadableAmount() function creates the amount of the smallest unit of a token from the full unit amount and the decimals.

The result of the call is the number of output tokens you'd receive for the quoted swap.

It should be noted that quoteExactInputSingle is only 1 of 4 different methods that the quoter offers:

  1. quoteExactInputSingle - given the amount you want to swap, produces a quote for the amount out for a swap of a single pool
  2. quoteExactInput - given the amount you want to swap, produces a quote for the amount out for a swap over multiple pools
  3. quoteExactOutputSingle - given the amount you want to get out, produces a quote for the amount in for a swap over a single pool
  4. quoteExactOutput - given the amount you want to get out, produces a quote for the amount in for a swap over multiple pools

If we want to trade two tokens that do not share a pool with each other, we will need to make swaps over multiple pools. This is where the quoteExactInput and quoteExactOutput methods come in. We will dive deeper into routing in the routing guide.

For the exactOutput and exactOutputSingle methods, we need to keep in mind that a pool can not give us more than the amount of Tokens it holds. If we try to get a quote on an output of 100 WETH from a Pool that only holds 50 WETH, the function call will fail.

Next Steps​

Now that you're able to make a quote, check out our next guide on trading using this quote!

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