Chainlink is a decentralized oracle network. It connects smart contracts to data and systems that live outside their own blockchain. A smart contract can only see what is recorded on its chain, so on its own it has no way to know a stock price, a sports result, the weather, or the value of one currency against another. Chainlink fills that gap by moving outside data onto the chain in a form a contract can read and act on.
The problem it solves is sometimes called the oracle problem. If a single source feeds a contract its outside data, that source becomes a weak point: it can fail, lie, or be tampered with, and the contract has no way to tell. Chainlink answers this by pulling the same information from many independent operators and combining their answers, so no single feed can quietly corrupt the result. The aim is data that reaches the chain without a trusted middleman.
The network was founded in 2017 by Sergey Nazarov and Steve Ellis. Ari Juels, a professor at Cornell University, co-authored the whitepaper that year. The network that serves smart contracts formally launched in 2019. Chainlink is described as blockchain-agnostic, meaning it is built to work across different chains rather than being tied to one. Its token, LINK, runs on Ethereum and follows the ERC-677 standard, an extension of the common ERC-20 format. LINK is used to pay node operators for their work and serves a role in network governance, and the project has a supply limit of one billion tokens.
LINK also backs a staking system. Holders can lock up tokens to help secure parts of the network and earn rewards for doing so honestly, which gives operators a financial reason to report accurate data. The code is open source under the MIT license and is written mainly in Solidity and Go.
Chainlink has added several pieces over the years. In 2018 it brought in Town Crier for connecting to data over standard web (HTTPS) connections. In 2020 it added DECO, which uses zero-knowledge proofs so a contract can confirm a fact about private data without exposing the data itself. In 2023 it launched the Cross-Chain Interoperability Protocol, known as CCIP, built to let blockchains and traditional finance systems pass messages and value between each other. Across decentralized finance, Chainlink price feeds are widely relied on to value collateral and to trigger the terms of a contract once a trade settles, which makes the network a piece of plumbing many applications quietly depend on.