Consuming Data Feeds using the Hardhat CLI

You can use Chainlink Data Feeds to connect your smart contracts to asset pricing data like the ETH / USD feed. These data feeds use data aggregated from many independent Chainlink node operators. Each price feed has an onchain address and functions that enable contracts to read pricing data from that address.

This guide shows you how to read Data Feeds and store the value onchain using Solidity. To learn how to read feeds offchain or use different languages, see the Using Data Feeds on EVM Chains guide. Alternatively, you can also learn how to use Data Feeds on Solana or StarkNet.

This CLI guide uses the Hardhat Framework so you can complete these steps using terminal commands rather than the web-based Remix IDE. If you prefer Remix or are unfamiliar with how to run terminal commands, read the Getting Started - Remix IDE guide instead.

The code for reading Data Feeds on Ethereum or other EVM-compatible blockchains is the same for each chain and each Data Feed types. You choose different types of feeds for different uses, but the request and response format are the same. The answer decimal length and expected value ranges might change depending on what feed you use.

Before you begin

This guide uses the Hardhat development environment to deploy and interact with the contracts. To learn more about Hardhat, read the Hardhat Documentation.

Requirements

• Git: Make sure you have Git installed. You can check your current version by running git --version in your terminal and download the latest version from the official Git website if necessary.
• Nodejs and npm: Install the latest release of Node.js 20. Optionally, you can use the nvm package to switch between Node.js versions with nvm use 20. To ensure you are running the correct version in a terminal, type node -v.

   $ node -v
   v20.11.0

• Testnet funds: This guide requires testnet ETH on Ethereum Sepolia. If necessary, go to faucets.chain.link and get testnet ETH on Ethereum Sepolia.

Examine the sample contract

This example contract obtains the latest price answer from the BTC / USD feed on the Sepolia testnet, but you can modify it to read any of the different Types of Data Feeds.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

import {AggregatorV3Interface} from "@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";

/**
 * THIS IS AN EXAMPLE CONTRACT THAT USES HARDCODED
 * VALUES FOR CLARITY.
 * THIS IS AN EXAMPLE CONTRACT THAT USES UN-AUDITED CODE.
 * DO NOT USE THIS CODE IN PRODUCTION.
 */

/**
 * If you are reading data feeds on L2 networks, you must
 * check the latest answer from the L2 Sequencer Uptime
 * Feed to ensure that the data is accurate in the event
 * of an L2 sequencer outage. See the
 * https://docs.chain.link/data-feeds/l2-sequencer-feeds
 * page for details.
 */

contract DataConsumerV3 {
    AggregatorV3Interface internal dataFeed;

    /**
     * Network: Sepolia
     * Aggregator: BTC/USD
     * Address: 0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43
     */
    constructor() {
        dataFeed = AggregatorV3Interface(
            0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43
        );
    }

    /**
     * Returns the latest answer.
     */
    function getChainlinkDataFeedLatestAnswer() public view returns (int) {
        // prettier-ignore
        (
            /* uint80 roundID */,
            int answer,
            /*uint startedAt*/,
            /*uint timeStamp*/,
            /*uint80 answeredInRound*/
        ) = dataFeed.latestRoundData();
        return answer;
    }
}

The contract has the following components:

• The import line imports an interface named AggregatorV3Interface. Interfaces define functions without their implementation, which leaves inheriting contracts to define the actual implementation themselves. In this case, AggregatorV3Interface defines that all v3 Aggregators have the function latestRoundData. You can see the complete code for the AggregatorV3Interface on GitHub.

• The constructor() {} initializes an interface object named dataFeed that uses AggregatorV3Interface and connects specifically to a proxy aggregator contract that is already deployed at 0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43. The interface allows your contract to run functions on that deployed aggregator contract.

• The getChainlinkDataFeedLatestAnswer() function calls your dataFeed object and runs the latestRoundData() function. When you deploy the contract, it initializes the dataFeed object to point to the aggregator at 0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43, which is the proxy address for the Sepolia BTC / USD data feed. Your contract connects to that address and executes the function. The aggregator connects with several oracle nodes and aggregates the pricing data from those nodes. The response from the aggregator includes several variables, but getChainlinkDataFeedLatestAnswer() returns only the answer variable.

Tutorial

Setup

1. Clone the repository that contains the Hardhat project setup for this guide. This repository contains the Solidity contract and the Hardhat configuration files you need to deploy and interact with the contract.

   git clone https://github.com/smartcontractkit/smart-contract-examples.git
   cd data-feeds/getting-started/hardhat

2. Install all the dependencies:

   npm install

3. Set an encryption password for your environment variables. This password needs to be set each time you create or restart a terminal shell session.

   npx env-enc set-pw

4. Set the required environment variables using the following command:

   npx env-enc set

   • PRIVATE_KEY: The private key for your testnet wallet that will deploy and interact with the contracts. If you use MetaMask, follow the instructions to Export a Private Key.
   • ETHEREUM_SEPOLIA_RPC_URL: The Remote Procedure Call (RPC) URL for the Ethereum Sepolia network. You can obtain one by creating an account on Alchemy or Infura and setting up an Ethereum Sepolia project.

Deploy the DataConsumerV3 contract

Execute the following command to deploy the DataConsumerV3 contract on the Ethereum Sepolia testnet:

npx hardhat deployDataConsumerV3 --network ethereumSepolia

After a few seconds, the transaction completes. Expect output similar to the following in your terminal:

ℹ Compiling contracts...
Compiled 2 Solidity files successfully (evm target: paris).
ℹ Starting deployment of DataConsumerV3 with account: 0x45C90FBb5acC1a5c156a401B56Fea55e69E7669d
✔ DataConsumerV3 deployed at: 0xcbEAC520915727e2cf242feA77EEEEEb319A43bB on ethereumSepolia

Save the deployed contract address. You will use this address later.

Get the latest answer from the aggregator contract

Execute the following command to get the latest answer from the aggregator contract:

npx hardhat getLatestAnswer --data-consumer-v3 <DataConsumerV3Address> --network ethereumSepolia

Replace <DataConsumerV3Address> with the address of the DataConsumerV3 contract you saved earlier.

Expect output similar to the following in your terminal:

✔ Latest BTC / USD Data Feed answer: 6292416053902

In this example, the answer is the latest price. The returned answer is an integer, so it is missing its decimal point. You can find the correct number of decimal places for this answer on the Price Feed addresses page by clicking the Show more details checkbox. The answer on the BTC / USD feed uses 8 decimal places, so an answer of 6292416053902 indicates a BTC / USD price of 62924.16053902. Each feed uses a different number of decimal places for answers.