From 04d6d0b03ec1c35ff4471bcb1ddeeb97a370d1a9 Mon Sep 17 00:00:00 2001 From: Robin Roy <66296664+robin-rrt@users.noreply.github.com> Date: Mon, 27 Jul 2026 22:37:35 +0400 Subject: [PATCH 1/4] add foundry and hardhat guides for DF getting started --- .../Foundry/DeployAndReadDataConsumerV3.s.sol | 59 + .../Hardhat/DeployAndReadDataConsumerV3.js | 47 + .../data-feeds/getting-started-foundry.mdx | 247 ++++ .../data-feeds/getting-started-hardhat.mdx | 313 +++++ src/content/data-feeds/getting-started.mdx | 234 +++- src/content/data-feeds/llms-full.txt | 1063 ++++++++++++++++- 6 files changed, 1889 insertions(+), 74 deletions(-) create mode 100644 public/samples/DataFeeds/Foundry/DeployAndReadDataConsumerV3.s.sol create mode 100644 public/samples/DataFeeds/Hardhat/DeployAndReadDataConsumerV3.js create mode 100644 src/content/data-feeds/getting-started-foundry.mdx create mode 100644 src/content/data-feeds/getting-started-hardhat.mdx diff --git a/public/samples/DataFeeds/Foundry/DeployAndReadDataConsumerV3.s.sol b/public/samples/DataFeeds/Foundry/DeployAndReadDataConsumerV3.s.sol new file mode 100644 index 00000000000..8c4ff0ab527 --- /dev/null +++ b/public/samples/DataFeeds/Foundry/DeployAndReadDataConsumerV3.s.sol @@ -0,0 +1,59 @@ +// SPDX-License-Identifier: MIT +pragma solidity ^0.8.7; + +/* solhint-disable no-console */ + +import {DataConsumerV3} from "../../src/DataFeeds/DataConsumerV3.sol"; +import {AggregatorV3Interface} from "@chainlink/contracts/src/v0.8/shared/interfaces/AggregatorV3Interface.sol"; +import {Script} from "forge-std/Script.sol"; +import {console2} from "forge-std/console2.sol"; + +/** + * 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. + * + * Deploy DataConsumerV3 and read the latest BTC/USD price on Sepolia. + * + * Usage: + * forge script script/DataFeeds/DeployAndReadDataConsumerV3.s.sol \ + * --rpc-url $SEPOLIA_RPC_URL \ + * --broadcast \ + * --private-key $PRIVATE_KEY + */ +contract DeployAndReadDataConsumerV3 is Script { + // Sepolia BTC / USD price feed proxy address + address public constant SEPOLIA_BTC_USD = 0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43; + + function run() public { + vm.startBroadcast(); + + // 1. Deploy the consumer contract + DataConsumerV3 consumer = new DataConsumerV3(); + console2.log("DataConsumerV3 deployed at:", address(consumer)); + + vm.stopBroadcast(); + + // 2. Read the latest price through the consumer + int256 answer = consumer.getChainlinkDataFeedLatestAnswer(); + console2.log("Latest answer (raw):", uint256(answer)); + + // 3. Read decimals directly from the feed to scale the answer + uint8 decimals = AggregatorV3Interface(SEPOLIA_BTC_USD).decimals(); + console2.log("Decimals:", decimals); + console2.log("Latest price (scaled): %s", _scale(answer, decimals)); + } + + function _scale( + int256 answer, + uint8 decimals + ) internal pure returns (string memory) { + // Convert the integer answer to a human-readable price string. + // For 8 decimals, 3030914000000 -> "30309.14000000" + uint256 magnitude = uint256(answer); + uint256 base = 10 ** decimals; + uint256 whole = magnitude / base; + uint256 fraction = magnitude % base; + return string.concat(vm.toString(whole), ".", vm.toString(fraction)); + } +} diff --git a/public/samples/DataFeeds/Hardhat/DeployAndReadDataConsumerV3.js b/public/samples/DataFeeds/Hardhat/DeployAndReadDataConsumerV3.js new file mode 100644 index 00000000000..d9f19406c8e --- /dev/null +++ b/public/samples/DataFeeds/Hardhat/DeployAndReadDataConsumerV3.js @@ -0,0 +1,47 @@ +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) +}) diff --git a/src/content/data-feeds/getting-started-foundry.mdx b/src/content/data-feeds/getting-started-foundry.mdx new file mode 100644 index 00000000000..21b4b165ebd --- /dev/null +++ b/src/content/data-feeds/getting-started-foundry.mdx @@ -0,0 +1,247 @@ +--- +section: dataFeeds +date: Last Modified +title: "Getting Started with Data Feeds (using Foundry)" +metadata: + title: "Getting Started with Chainlink Data Feeds — Foundry" + description: "Read Chainlink Data Feeds using the Foundry CLI. Deploy a consumer contract on Sepolia with forge, read the BTC/USD price feed onchain, and read feeds offchain with cast call." + excerpt: "Deploy a consumer contract with forge and read Data Feeds with cast" + image: "/files/1a63254-link.png" + difficulty: "beginner" + estimatedTime: "15 minutes" +whatsnext: + { + "Read Data Feeds on other EVM chains and with other Web3 libraries": "/data-feeds/using-data-feeds", + "Retrieve Historical Price Data": "/data-feeds/historical-data", + "Read the Data Feeds API Reference": "/data-feeds/api-reference", + "Find Price Feed addresses on other networks": "/data-feeds/price-feeds/addresses", + } +--- + +import { Aside, CodeSample, CopyText, PageTabs } from "@components" + +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, for example the [ETH / USD feed](https://data.chain.link/feeds/ethereum/mainnet/eth-usd). + +This guide walks you through reading a Data Feed end-to-end using the [Foundry](https://book.getfoundry.sh/) CLI. You'll deploy a consumer contract on the Sepolia testnet with `forge`, read the BTC / USD price feed onchain, and read the same feed offchain with `cast call`. + +## What you'll do + +- Deploy a Solidity consumer contract that reads the BTC / USD price feed on Sepolia using `forge script`. +- Retrieve the latest price onchain by calling the consumer contract with `cast call`. +- Read the same feed offchain directly from the feed proxy with `cast call` — no consumer contract required. +- Learn the key safety checks to apply before moving to production. + +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. + + + +{/* prettier-ignore */} + + +## 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: + +- [Foundry](https://book.getfoundry.sh/getting-started/installation) installed (`forge`, `cast`). +- 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. + +{/* prettier-ignore */} + + +## Step 1: 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). + + + +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) — the Solidity interface that every Chainlink v3 price feed proxy implements. 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 . 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 , 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. + +## Step 2: Set up a Foundry project + +1. Create a new Foundry project and add the Chainlink contracts dependency: + + ```bash + forge init data-feeds-quickstart + cd data-feeds-quickstart + forge install smartcontractkit/chainlink-evm@contracts-v1.5.0 + ``` + +1. Add this remapping to `remappings.txt` so Solidity can resolve `@chainlink/contracts`: + + ```text + @chainlink/contracts/=lib/chainlink-evm/contracts/ + ``` + + You can write it with a single command: + + ```bash + echo '@chainlink/contracts/=lib/chainlink-evm/contracts/' > remappings.txt + ``` + +1. Create the directories for the sample consumer contract and deploy script: + + ```bash + mkdir -p src/DataFeeds script/DataFeeds + ``` + +1. Create the following files and paste in the code from the rendered code blocks on this page: + + - Create `src/DataFeeds/DataConsumerV3.sol` and paste in the contract from [Step 1: Examine the sample contract](#step-1-examine-the-sample-contract). + - Create `script/DataFeeds/DeployAndReadDataConsumerV3.s.sol` and paste in the script from [Step 3: Deploy the contract with a Forge script](#step-3-deploy-the-contract-with-a-forge-script). + + Make sure the filenames match exactly — Foundry looks for the contract in `src/` and the script in `script/`. + +1. Verify the project compiles: + + ```bash + forge build + ``` + + You should see `Compiler run successful`. If you see an import error, double-check the `remappings.txt` line from step 2. + +## Step 3: Deploy the contract with a Forge script + +The deploy script (`script/DataFeeds/DeployAndReadDataConsumerV3.s.sol`) deploys `DataConsumerV3` and immediately reads the latest price through it. For reference, here is the script: + + + +Run it against Sepolia. Replace `$SEPOLIA_RPC_URL` and `$PRIVATE_KEY` with your own values: + +```bash +forge script script/DataFeeds/DeployAndReadDataConsumerV3.s.sol \ + --rpc-url $SEPOLIA_RPC_URL \ + --broadcast \ + --private-key $PRIVATE_KEY +``` + +The script logs the deployed contract address, the raw integer answer, the feed's decimals, and the human-readable price. Save the deployed contract address for the next step. + +{/* prettier-ignore */} + + +## Step 4: Read the latest price onchain + +Use `cast call` to read the latest answer through your deployed consumer. Replace `$CONSUMER_ADDRESS` with the address logged by the deploy script: + +```bash +cast call $CONSUMER_ADDRESS "getChainlinkDataFeedLatestAnswer()(int256)" --rpc-url $SEPOLIA_RPC_URL +``` + +Read the feed's decimals directly to scale the answer yourself: + +```bash +cast call 0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43 "decimals()(uint8)" --rpc-url $SEPOLIA_RPC_URL +``` + +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. + +{/* prettier-ignore */} + + +## Step 5: Read the same feed offchain (no consumer contract required) + +You can also read Data Feeds directly from the feed proxy without deploying a consumer contract. This is useful for backends, bots, dashboards, and pre-trade checks. + +Read the latest answer with a single `cast call` against the feed proxy at : + +```bash +cast call 0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43 "latestRoundData()(uint80,int256,uint256,uint256,uint80)" --rpc-url $SEPOLIA_RPC_URL +``` + +Read the decimals so you can scale the answer: + +```bash +cast call 0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43 "decimals()(uint8)" --rpc-url $SEPOLIA_RPC_URL +``` + +The BTC / USD feed returns `8` for decimals. Divide the raw integer answer by `10 ** decimals` to get the human-readable price. For example, an answer of `3030914000000` with 8 decimals is `30309.14` USD. + +## 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: + + + +### 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 `cast` or ethers.js. See [Step 5: Read the same feed offchain](#step-5-read-the-same-feed-offchain-no-consumer-contract-required) on this page, or the [Hardhat](/data-feeds/getting-started-hardhat) guide. + +| | 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 | diff --git a/src/content/data-feeds/getting-started-hardhat.mdx b/src/content/data-feeds/getting-started-hardhat.mdx new file mode 100644 index 00000000000..fce3cd36727 --- /dev/null +++ b/src/content/data-feeds/getting-started-hardhat.mdx @@ -0,0 +1,313 @@ +--- +section: dataFeeds +date: Last Modified +title: "Getting Started with Data Feeds (using Hardhat)" +metadata: + title: "Getting Started with Chainlink Data Feeds — Hardhat" + description: "Read Chainlink Data Feeds in a smart contract using Hardhat. Deploy a consumer contract on Sepolia with ethers.js, read the BTC/USD price feed onchain, and read feeds offchain from a script." + excerpt: "Deploy a consumer contract with Hardhat and read Data Feeds onchain and offchain" + image: "/files/1a63254-link.png" + difficulty: "beginner" + estimatedTime: "15 minutes" +whatsnext: + { + "Read Data Feeds on other EVM chains and with other Web3 libraries": "/data-feeds/using-data-feeds", + "Retrieve Historical Price Data": "/data-feeds/historical-data", + "Read the Data Feeds API Reference": "/data-feeds/api-reference", + "Find Price Feed addresses on other networks": "/data-feeds/price-feeds/addresses", + } +--- + +import { Aside, CodeSample, CopyText, PageTabs } from "@components" + +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, for example the [ETH / USD feed](https://data.chain.link/feeds/ethereum/mainnet/eth-usd). + +This guide walks you through reading a Data Feed end-to-end using [Hardhat 3](https://hardhat.org/) and [ethers.js](https://docs.ethers.org/). You'll deploy a consumer contract on the Sepolia testnet, read the BTC / USD price feed onchain, and read the same feed offchain from a script. + +## What you'll do + +- Deploy a Solidity consumer contract that reads the BTC / USD price feed on Sepolia using a Hardhat script. +- Retrieve the latest price onchain by calling the consumer contract. +- Read the same feed offchain directly from the feed proxy with ethers.js — no consumer contract required. +- Learn the key safety checks to apply before moving to production. + +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. + + + +{/* prettier-ignore */} + + +## 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. + +{/* prettier-ignore */} + + +{/* prettier-ignore */} + + +## Step 1: 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). + + + +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) — the Solidity interface that every Chainlink v3 price feed proxy implements. 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 . 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 , 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. + +## Step 2: Set up a Hardhat project + +This guide uses [Hardhat 3](https://hardhat.org/) with the Mocha + Ethers.js toolbox. Hardhat 3 is ESM-first and uses a declarative config with [configuration variables](https://hardhat.org/docs/guides/configuration-variables) for secrets. + +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 + ``` + +1. Install the Chainlink contracts npm package: + + ```bash + npm install @chainlink/contracts + ``` + + Hardhat resolves `@chainlink/contracts` from `node_modules` automatically — no remapping file is needed (unlike Foundry). + +1. Create the directories for the sample consumer contract and deployment script: + + ```bash + mkdir -p contracts/DataFeeds scripts/DataFeeds + ``` + +1. 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 1: Examine the sample contract](#step-1-examine-the-sample-contract). + - Create `scripts/DataFeeds/DeployAndReadDataConsumerV3.js` and paste in the script from [Step 3: Deploy the contract with a Hardhat script](#step-3-deploy-the-contract-with-a-hardhat-script). + + Make sure the filenames match exactly — Hardhat looks for the contract in `contracts/` and the script in `scripts/`. The template's sample `Counter.sol`, `Counter.t.sol`, and `send-op-tx.ts` files can stay — the compiler version in the next step is compatible with them. + +1. Configure your `hardhat.config.ts` to compile the Chainlink contracts and use Sepolia. Replace its contents with: + + ```typescript + 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")], + }, + }, + }) + ``` + +1. 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 + ``` + +1. 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/`. + +## Step 3: Deploy the contract with a 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: + + + +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._** + +## Step 4: Read the latest price onchain + +You can read the latest price through your deployed consumer contract using a one-off Hardhat console, or from any ethers.js script. Using the Hardhat console: + +```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 Step 3: + +```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. + +{/* prettier-ignore */} + + +## Step 5: Read the same feed offchain (no consumer contract required) + +You can also read Data Feeds directly from the feed proxy without deploying a consumer contract. This is useful for backends, bots, dashboards, and pre-trade checks. No consumer contract is required — the feed proxy is a public contract and `latestRoundData()` is a `view` function, so anyone can call it directly. + +Use the same Hardhat console from Step 4 (or open a new one with `npx hardhat console --network sepolia` and run `const { ethers } = await network.create()` first). This time, point `ethers.getContractAt` at the **feed proxy** instead of your deployed consumer: + +```javascript +const feed = await ethers.getContractAt( + [ + "function latestRoundData() view returns (uint80 roundId, int256 answer, uint256 startedAt, uint256 updatedAt, uint80 answeredInRound)", + "function decimals() view returns (uint8)", + ], + "0x1b44F3514812d835EB1BDB0acB33d3fA3351Ee43" +) +const { answer } = await feed.latestRoundData() +const decimals = await feed.decimals() +console.log("Latest answer (raw):", answer.toString()) +console.log("Price (USD):", Number(answer) / 10 ** Number(decimals)) +``` + +The BTC / USD feed returns `8` for decimals. Divide the raw integer answer by `10 ** decimals` to get the human-readable price. For example, an answer of `3030914000000` with 8 decimals is `30309.14` USD. + +## 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: + + + +### 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 5: Read the same feed offchain](#step-5-read-the-same-feed-offchain-no-consumer-contract-required) 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 | diff --git a/src/content/data-feeds/getting-started.mdx b/src/content/data-feeds/getting-started.mdx index b16bb304e4b..739fc0ce15f 100644 --- a/src/content/data-feeds/getting-started.mdx +++ b/src/content/data-feeds/getting-started.mdx @@ -1,28 +1,62 @@ --- section: dataFeeds date: Last Modified -title: "Consuming Data Feeds" +title: "Getting Started with Data Feeds" +metadata: + title: "Getting Started with Chainlink Data Feeds — Low code (Remix)" + description: "Read Chainlink Data Feeds in a smart contract using the Remix IDE. Deploy a consumer contract on Sepolia and read the BTC/USD price feed — no local installation required." + excerpt: "Deploy a consumer contract and read Data Feeds onchain using Remix" + image: "/files/1a63254-link.png" + difficulty: "beginner" + estimatedTime: "15 minutes" + datePublished: "2026-07-22" + lastModified: "2026-07-22" whatsnext: { - "See examples for how to read feeds onchain and offchain": "/data-feeds/using-data-feeds", - "Learn how to retrieve Historical Price Data": "/data-feeds/historical-data", + "Read Data Feeds on other EVM chains and with other Web3 libraries": "/data-feeds/using-data-feeds", + "Retrieve Historical Price Data": "/data-feeds/historical-data", "Read the Data Feeds API Reference": "/data-feeds/api-reference", + "Find Price Feed addresses on other networks": "/data-feeds/price-feeds/addresses", } -metadata: - title: "Consuming Data Feeds" - description: "Learn how to consume Chainlink Data Feeds in your smart contracts." - excerpt: "Smart Contracts and Chainlink" - image: "/files/1a63254-link.png" --- -import { Aside, CodeSample } from "@components" +import { Aside, CodeSample, CopyText, ClickToZoom, PageTabs } from "@components" + +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, for example the [ETH / USD feed](https://data.chain.link/feeds/ethereum/mainnet/eth-usd). -You can use Chainlink Data Feeds to connect your smart contracts to asset pricing data like the [ETH / USD feed](https://data.chain.link/feeds/ethereum/mainnet/eth-usd). 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 walks you through reading a Data Feed end-to-end using the [Remix IDE](https://remix.ethereum.org/). You'll deploy a consumer contract on the Sepolia testnet and read the BTC / USD price feed onchain. -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](/data-feeds/using-data-feeds) guide. Alternatively, you can also learn how to use Data Feeds on [Solana](/data-feeds/solana) or [StarkNet](/data-feeds/starknet). +## What you'll do -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. +- Deploy a Solidity consumer contract that reads the BTC / USD price feed on Sepolia. +- Retrieve the latest price onchain by calling the consumer contract. +- Learn the key safety checks to apply before moving to production. +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. + + + +{/* prettier-ignore */}