# Getting Started with Data Feeds (using Hardhat)
Source: https://docs.chain.link/data-feeds/getting-started-hardhat

> For the complete documentation index, see [llms.txt](/llms.txt).

Chainlink Data Feeds are the fastest way to connect your smart contracts to real-world data such as asset prices, reserve balances, and L2 sequencer health. Each feed is aggregated by many independent Chainlink node operators and published onchain through a decentralized oracle network, giving your contracts a reliable, manipulation-resistant source of data.

Each price feed has an onchain address and functions that enable contracts to read pricing data from that address.

In this guide you will fetch the pricing data from a price feed, for example the [BTC / USD feed](https://data.chain.link/feeds/ethereum/mainnet/btc-usd).

## What you'll do

- Retrieve latest pricing data from the BTC / USD price feed offchain directly from the feed proxy. *(Offchain methods are useful for backends, bots, dashboards, and pre-trade checks)*
- Deploy and retrieve the latest price onchain using a Solidity consumer contract that reads the BTC / USD price feed on Sepolia. *(Onchain methods are useful for when you need to apply smart contract logic in your application based on the pricing data.)*
- Learn the key safety checks to apply before moving to production.

**Note:** The code for reading Data Feeds on Ethereum and other EVM-compatible blockchains is the same for every chain and every feed type. You choose different feeds for different use cases, but the request and response format is always the same. The answer's decimal length and expected value range may differ depending on the feed.

> **CAUTION: Using Data Feeds on L2 networks**
>
> If you are using Chainlink Data Feeds on L2 networks like Arbitrum, OP, and Metis, you must also 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 [L2 Sequencer Uptime Feeds](/data-feeds/l2-sequencer-feeds) page to learn how to use Data Feeds on L2
> networks.

## Before you begin

If you are new to smart contract development, complete the [Deploy Your First Smart Contract](/quickstarts/deploy-your-first-contract) quickstart first.

You will need:

- [Node.js](https://nodejs.org/) v22.13.0 or later (required by Hardhat 3).
- A funded wallet on the **Sepolia** testnet. Get testnet ETH from a [Sepolia faucet](/resources/link-token-contracts/#sepolia-testnet).
- A Sepolia RPC URL (e.g. from a [node provider](https://ethereum.org/en/developers/docs/nodes-and-clients/nodes-as-a-service/)).
- A funded deployer private key for Sepolia.

> **CAUTION: Keep your private key safe**
>
> Never commit your private key to version control or hardcode it in a script. This guide uses Hardhat 3
> [configuration variables](https://hardhat.org/docs/guides/configuration-variables), which read secrets from
> environment variables or an encrypted keystore — no `.env` file required. If you do use a `.env` file, add it to
> your `.gitignore`.

> **NOTE: Why a proxy?**
>
> Consumer contracts call a *proxy* contract, which forwards reads to the current *aggregator*. When Chainlink
> upgrades an aggregator, the proxy is repointed to the new implementation and your consumer contract keeps working
> unchanged. Always read from the proxy address listed on the
> [Price Feed Addresses](/data-feeds/price-feeds/addresses) page, not from the underlying aggregator.

## Getting the feed address

Before we even begin, we need to know the address of the feed we want to read. The [Price Feed Addresses](/data-feeds/price-feeds/addresses) page lists all the feeds available on each network. For this guide, we will use the BTC / USD feed on Sepolia, with the proxy address: 0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43

## Retrieving the price data from the feed

<Accordion title="Fetching price data onchain using a consumer contract" number={2}>
  <Accordion title="Examine the sample contract" number={2.1} contentReference="examine-the-sample-contract">
    The example contract below reads the latest answer from the [BTC / USD feed](/data-feeds/price-feeds/addresses) on Sepolia. You can modify it to read any of the [Types of Data Feeds](/data-feeds#types-of-data-feeds).


    ```solidity filename='contracts/DataFeeds/DataConsumerV3.sol'
    // SPDX-License-Identifier: MIT
    pragma solidity ^0.8.7;

    import {AggregatorV3Interface} from "@chainlink/contracts/src/v0.8/shared/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 (int256) {
        // prettier-ignore
        (
          /* uint80 roundId */
          ,
          int256 answer,
          /*uint256 startedAt*/
          ,
          /*uint256 updatedAt*/
          ,
          /*uint80 answeredInRound*/
        ) = dataFeed.latestRoundData();
        return answer;
      }
    }
    ```

    The contract has the following components:

    - The `import` line brings in [`AggregatorV3Interface`](https://github.com/smartcontractkit/chainlink-evm/blob/contracts-v1.5.0/contracts/src/v0.8/shared/interfaces/AggregatorV3Interface.sol)
      - It exposes `latestRoundData()`, `getRoundData()`, `decimals()`, and `version()`. The sample uses `latestRoundData` to fetch the current price.
    - The `constructor()`
      - Initializes a `dataFeed` object that uses `AggregatorV3Interface` pointing at the proxy aggregator deployed at <CopyText text="0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43" code />.
      - This is the proxy address for the Sepolia `BTC / USD` feed. The proxy lets the aggregator be upgraded without breaking consumer contracts.
    - The `getChainlinkDataFeedLatestAnswer()` function
      - Calls your `dataFeed` object and runs the `latestRoundData()` function and returns the `answer` variable.
      - When you deploy the contract, it initializes the `dataFeed` object to point to the aggregator at <CopyText text="0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43" code />, 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. The full response includes `roundId`, `startedAt`, `updatedAt`, and `answeredInRound` — see the [API Reference](/data-feeds/api-reference) for details.
  </Accordion>

  <Accordion title="Set up a Hardhat project" number={2.2}>
    1. Create a new Hardhat 3 project and initialize it with the Mocha + Ethers.js template:

       ```bash
       mkdir data-feeds-quickstart
       cd data-feeds-quickstart
       npm init -y
       npm install --save-dev hardhat
       npx hardhat --init --template mocha-ethers
       ```

    2. Install the Chainlink contracts npm package:

       ```bash
       npm install @chainlink/contracts
       ```

       Hardhat resolves `@chainlink/contracts` from `node_modules` automatically — no remapping file needed (unlike Foundry).

    3. Create the directories for the sample consumer contract and deploy script:

       ```bash
       mkdir -p contracts/DataFeeds scripts/DataFeeds
       ```

    4. Create the following files and paste in the code from the rendered code blocks on this page:

       - Create `contracts/DataFeeds/DataConsumerV3.sol` and paste in the contract from [Step 2.1: Examine the sample contract](#examine-the-sample-contract).
       - Create `scripts/DataFeeds/DeployAndReadDataConsumerV3.js` and paste in the script from [Step 2.3: Deploy the contract with a Hardhat script](#deploy-with-hardhat-script).

       Make sure the filenames match exactly — Hardhat looks for the contract in `contracts/` and the script in `scripts/`.

    5. Configure your `hardhat.config.ts` to compile the Chainlink contracts and use Sepolia. Replace its contents with:

       ```typescript filename='hardhat.config.ts'
       import hardhatToolboxMochaEthersPlugin from "@nomicfoundation/hardhat-toolbox-mocha-ethers"
       import { configVariable, defineConfig } from "hardhat/config"

       export default defineConfig({
         plugins: [hardhatToolboxMochaEthersPlugin],
         solidity: {
           profiles: {
             default: {
               version: "0.8.28",
             },
             production: {
               version: "0.8.28",
               settings: {
                 optimizer: { enabled: true, runs: 200 },
               },
             },
           },
         },
         networks: {
           hardhatMainnet: {
             type: "edr-simulated",
             chainType: "l1",
           },
           hardhatOp: {
             type: "edr-simulated",
             chainType: "op",
           },
           sepolia: {
             type: "http",
             chainType: "l1",
             url: configVariable("SEPOLIA_RPC_URL"),
             accounts: [configVariable("SEPOLIA_PRIVATE_KEY")],
           },
         },
       })
       ```

    6. Set your Sepolia RPC URL and deployer private key as environment variables (or store them in the Hardhat keystore as noted above):

       ```bash
       export SEPOLIA_RPC_URL=your_sepolia_rpc_url
       export SEPOLIA_PRIVATE_KEY=your_deployer_private_key
       ```

    7. Verify the project compiles:

       ```bash
       npx hardhat compile
       ```

       You should see `Compiled 2 Solidity files with solc 0.8.28`. If you see an import error, check that `@chainlink/contracts` is installed (step 2) and that the contract is under `contracts/`.
  </Accordion>

  <Accordion title="Deploy the contract with a Hardhat script" number={2.3} contentReference="deploy-with-hardhat-script">
    The deploy script (`scripts/DataFeeds/DeployAndReadDataConsumerV3.js`) deploys `DataConsumerV3` and immediately reads the latest price through it. For reference, here is the script:


    ```javascript filename='scripts/DataFeeds/DeployAndReadDataConsumerV3.js'
    import { network } from "hardhat"

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

    const { ethers } = await network.create()

    async function main() {
      // 1. Deploy the DataConsumerV3 contract
      const consumer = await ethers.deployContract("DataConsumerV3")
      await consumer.waitForDeployment()

      const consumerAddress = await consumer.getAddress()
      console.log("DataConsumerV3 deployed at:", consumerAddress)

      // 2. Read the latest price through the consumer contract
      const answer = await consumer.getChainlinkDataFeedLatestAnswer()
      console.log("Latest answer (raw):", answer.toString())

      // 3. Read decimals directly from the feed to scale the answer
      // Sepolia BTC / USD price feed proxy address
      const feedAddress = "0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43"
      const AggregatorV3Interface = [
        {
          inputs: [],
          name: "decimals",
          outputs: [{ internalType: "uint8", name: "", type: "uint8" }],
          stateMutability: "view",
          type: "function",
        },
      ]
      const feed = await ethers.getContractAt(AggregatorV3Interface, feedAddress)
      const decimals = await feed.decimals()
      console.log("Decimals:", decimals)

      // 4. Scale and print the human-readable price
      const scaled = Number(answer) / 10 ** Number(decimals)
      console.log("Latest price (USD):", scaled)
    }

    main().catch((error) => {
      console.error(error)
      process.exit(1)
    })
    ```

    Run it against Sepolia:

    ```bash
    npx hardhat run scripts/DataFeeds/DeployAndReadDataConsumerV3.js --network sepolia
    ```

    The script logs the deployed contract address, the raw integer answer, the feed's decimals, and the human-readable price.

    Save the deployed contract address for the next step.
  </Accordion>

  <Accordion title="Read the latest price onchain" number={2.4}>
    Open a Hardhat console against Sepolia:

    ```bash
    npx hardhat console --network sepolia
    ```

    In Hardhat 3, obtain `ethers` from `network.create()` at the prompt, then read through your consumer. Replace `0xYOUR_CONSUMER_ADDRESS` with the address the deploy script logged in the previous step:

    ```javascript
    const { ethers } = await network.create()
    const consumer = await ethers.getContractAt("DataConsumerV3", "0xYOUR_CONSUMER_ADDRESS")
    const answer = await consumer.getChainlinkDataFeedLatestAnswer()
    console.log("Latest answer (raw):", answer.toString())
    ```

    Read the feed's decimals directly to scale the answer yourself:

    ```javascript
    const feed = await ethers.getContractAt(
      ["function decimals() view returns (uint8)"],
      "0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43"
    )
    const decimals = await feed.decimals()
    console.log("Decimals:", decimals)
    ```

    The BTC / USD feed returns `8` for decimals. To convert the raw integer answer to a human-readable price, divide by `10 ** decimals`. For example, an answer of `3030914000000` with 8 decimals is `30309.14` USD.


    > **TIP: Always scale by `decimals()`**
    >
    > Never hardcode the decimal count. Call `decimals()` on the feed and scale the answer programmatically. This keeps
    > your contract correct if you later point it at a feed with a different precision (e.g., some feeds use 18 decimals).
  </Accordion>
</Accordion>

## Before you go to production

The example intentionally omits the safety checks a production integration needs. Before shipping, review the following points and the [Developer Responsibilities](/data-feeds/developer-responsibilities) page.

### Check `updatedAt` and staleness

`latestRoundData()` returns `updatedAt` (the timestamp of the latest round) and `answeredInRound` (the round in which the answer was finalized). Always verify the feed is fresh:

```solidity
(uint80 roundId, int256 answer, , uint256 updatedAt, uint80 answeredInRound) = dataFeed.latestRoundData();

require(answeredInRound >= roundId, "Stale price");
require(block.timestamp - updatedAt < TIMEOUT, "Stale price");
```

Choose a `TIMEOUT` that matches your application's risk tolerance — shorter for trading, longer for less time-sensitive use cases.

### Use the right feed for your asset

Not all feeds are equal. Low-liquidity assets are more exposed to market manipulation. Review [Selecting Quality Data Feeds](/data-feeds/selecting-data-feeds) and the [Data Feed Categories](/data-feeds/selecting-data-feeds#data-feed-categories) before choosing a feed.

### Handle L2 sequencer risk

On L2s, a sequencer outage can cause stale or incorrect prices. Always pair L2 price feeds with a check on the [L2 Sequencer Uptime Feed](/data-feeds/l2-sequencer-feeds). The `DataConsumerWithSequencerCheck` sample shows the pattern. Try it out in Remix below:

[Open DataConsumerWithSequencerCheck.sol in Remix](https://remix.ethereum.org/#url=https://docs.chain.link/samples/DataFeeds/DataConsumerWithSequencerCheck.sol)

### Audit your integration

The sample code is unaudited and hardcodes values for clarity. Before production, complete your own audit, review your dependencies, and apply the risk-mitigation practices described in [Developer Responsibilities](/data-feeds/developer-responsibilities).

## FAQ

### Do I need a consumer contract to read a Data Feed?

**Only if another smart contract needs the price onchain.** A consumer contract exists to wrap a feed read in your own contract's logic so that *your other contracts* can use the price onchain — for collateral checks, settlements, circuit breakers, and so on. The read is atomic with your onchain action and verifiable on the blockchain.

If you only need the price in an offchain system (a backend, bot, dashboard, or pre-trade check), you do **not** need a consumer contract. The feed proxy is a public contract and `latestRoundData()` is a `view` function — anyone can call it directly from a script using ethers.js, viem, or `cast`. See [Step 1: Fetching price data offchain](#read-offchain) on this page.

|                                 | Consumer contract (onchain)           | Direct read (offchain)               |
| ------------------------------- | ------------------------------------- | ------------------------------------ |
| **Who needs the price?**        | Another smart contract                | A script, backend, bot, or dashboard |
| **Gas cost?**                   | Pay to deploy + gas for onchain reads | Free (view calls from a script)      |
| **Deployment required?**        | Yes                                   | No                                   |
| **Atomic with onchain action?** | Yes                                   | No                                   |