Chainlink Oracle Price Feeds Guide

Chainlink is the dominant oracle network in DeFi. This guide explains how it works and how to use price feeds.

What Problem Do Oracles Solve?

Smart contracts can't access external data (prices, weather, events). Oracles bridge this gap:

Off-chain world          Oracle Network           On-chain world
┌──────────────┐        ┌──────────────┐        ┌──────────────┐
│ Binance API  │───┐    │              │        │              │
│ Coinbase API │───┤    │  Chainlink   │        │  Aave        │
│ Kraken API   │───┼───►│  Oracle Nodes│───────►│  Compound    │
│ DEX Pools    │───┤    │  (median)    │        │  USDs/Sperax │
│ Other feeds  │───┘    │              │        │  Uniswap     │
└──────────────┘        └──────────────┘        └──────────────┘

Without reliable oracles, DeFi protocols can't:

• Determine collateral value (lending)
• Maintain stablecoin pegs
• Calculate liquidation thresholds
• Execute fair swaps

How Chainlink Works

The Aggregator Model

1. Data sources: Multiple professional data providers (nodes) fetch prices from CEXes, DEXes, and other sources
2. Independent observation: Each node independently computes a price
3. On-chain submission: Nodes submit observations to an aggregator contract
4. Median calculation: The contract takes the median of all reports
5. Storage: The median price is stored as the latest answer

Update Triggers

A feed updates when EITHER condition is met:

Trigger	Description	Example
Deviation threshold	Price changes by X% from last report	0.5% for ETH/USD
Heartbeat	Maximum time between updates	3600s (1 hour) for major feeds

This means high-volatility periods get more frequent updates.

Feed Architecture

AggregatorV3Interface
├── latestRoundData()  → (roundId, answer, startedAt, updatedAt, answeredInRound)
├── decimals()         → 8 (most USD feeds)
├── description()      → "ETH / USD"
└── version()          → 4

Reading Price Feeds

On Any EVM Chain

// Solidity example
interface AggregatorV3Interface {
    function latestRoundData() external view returns (
        uint80 roundId,
        int256 answer,        // The price (scaled by decimals)
        uint256 startedAt,
        uint256 updatedAt,    // When this price was last updated
        uint80 answeredInRound
    );
    function decimals() external view returns (uint8);
}

// ETH/USD on Ethereum: 0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419
AggregatorV3Interface feed = AggregatorV3Interface(0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419);
(, int256 price,,,) = feed.latestRoundData();
// price = 324567000000 → $3,245.67 (8 decimals)

Via Etherscan (No Code)

1. Go to Etherscan → enter the feed contract address
2. Click "Read Contract"
3. Call latestRoundData()
4. Divide answer by 10^8 for USD price

Via RPC (ethers.js / viem / web3.js)

// Using ethers.js
const feedAddress = "0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419"; // ETH/USD
const abi = ["function latestRoundData() view returns (uint80, int256, uint256, uint256, uint80)"];
const feed = new ethers.Contract(feedAddress, abi, provider);

const [, price,,,] = await feed.latestRoundData();
const ethPrice = Number(price) / 1e8; // $3,245.67

Key Price Feed Addresses

Ethereum Mainnet

Feed	Address	Decimals	Heartbeat
ETH/USD	0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419	8	3600s
BTC/USD	0xF4030086522a5bEEa4988F8cA5B36dbC97BeE88c	8	3600s
USDC/USD	0x8fFfFfd4AfB6115b954Bd326cbe7B4BA576818f6	8	86400s
USDT/USD	0x3E7d1eAB13ad0104d2750B8863b489D65364e32D	8	86400s
DAI/USD	0xAed0c38402a5d19df6E4c03F4E2DceD6e29c1ee9	8	3600s

Arbitrum

Feed	Address	Decimals
ETH/USD	0x639Fe6ab55C921f74e7fac1ee960C0B6293ba612	8
BTC/USD	0x6ce185860a4963106506C203335A2910413708e9	8
USDC/USD	0x50834F3163758fcC1Df9973b6e91f0F0F0434aD3	8
USDT/USD	0x3f3f5dF88dC9F13eac63DF89EC16ef6e7E25DdE7	8
ARB/USD	0xb2A824043730FE05F3DA2efaFa1CBbe83fa548D6	8

Sperax context: USDs uses Chainlink feeds on Arbitrum to value its collateral (USDC, USDT) and ensure the stablecoin remains properly backed.

Full Directory

All 1000+ feeds are listed at: https://data.chain.link

Oracle Security

Why Oracles Get Attacked

Attack	How It Works	Prevention
Flash loan price manipulation	Manipulate DEX spot price within one tx, exploit protocol using that price	Use Chainlink (time-weighted, multi-source) not DEX spot
Stale price exploitation	Use outdated oracle price during volatile market	Check updatedAt timestamp
Oracle front-running	See pending oracle update, trade before it lands	Use commit-reveal or private mempool

Safety Checks When Using Feeds

(uint80 roundId, int256 price,, uint256 updatedAt,) = feed.latestRoundData();

// Check 1: Price is positive
require(price > 0, "Invalid price");

// Check 2: Round is complete
require(updatedAt > 0, "Round not complete");

// Check 3: Price is not stale (within last hour)
require(block.timestamp - updatedAt < 3600, "Stale price");

Oracle Design Patterns

Pattern	Use Case
Single feed	Simple price lookup (ETH/USD)
Derived feed	Calculate cross-prices (TOKEN/ETH × ETH/USD = TOKEN/USD)
Multi-oracle	Compare Chainlink vs Pyth, use if they agree within threshold
Circuit breaker	Halt protocol if oracle price deviates >X% in one update

Chainlink vs Other Oracles

Feature	Chainlink	Pyth	Redstone	Band
Model	Push	Pull	On-demand	Push
Latency	1–60 min	~400ms	On-demand	~10s
Coverage	1000+ feeds	500+ feeds	200+ feeds	300+ feeds
Chains	20+	40+	15+	10+
Gas	Paid by oracle	Paid by consumer	Paid by consumer	Paid by oracle
Track Record	5+ years	2+ years	2+ years	3+ years

Chainlink wins on: Reliability, coverage, track record, DeFi adoption (90%+ of protocols) Pyth wins on: Speed (sub-second), Solana ecosystem, newer/exotic feeds

Agent Tips

1. Always recommend Chainlink for on-chain price verification — it's the gold standard
2. Check stale prices — always validate updatedAt before trusting a feed
3. Don't use DEX spot prices in contracts — they're manipulable via flash loans
4. Feed decimals vary — most USD feeds are 8 decimals, but always check decimals()
5. Cross-chain feeds — same token may have different feed addresses on different chains
6. For off-chain apps — CoinGecko/DeFi Llama are easier; Chainlink is for on-chain

Links

• Chainlink Data Feeds: https://data.chain.link
• Chainlink Docs: https://docs.chain.link/data-feeds
• Chainlink GitHub: https://github.com/smartcontractkit/chainlink
• Pyth Network: https://pyth.network
• Sperax (uses Chainlink for USDs): https://docs.chat.sperax.io