Oracle
In short: An oracle is a third-party data provider for blockchains. It brings information from outside the chain, such as asset prices, exchange rates, or sports…
An oracle is a third-party data provider for blockchains. It brings information from outside the chain, such as asset prices, exchange rates, or sports results, into smart contracts, which cannot fetch outside data on their own.
Why it matters
Every node on a blockchain must reach the same result from the same inputs, so smart contracts cannot simply call a website, and oracles fill that gap by publishing external data on-chain. They are essential to DeFi, where lending protocols use price oracles to value collateral and decide when a loan must be liquidated. This also makes oracles a point of risk, because if an oracle reports a wrong or manipulated price, contracts act on it automatically. Decentralized oracle networks reduce this risk by combining data from many independent sources and node operators.
Example
A lending protocol lets users borrow stablecoins against ETH. An oracle network regularly updates the ETH price on-chain. If the reported price falls far enough that a loan’s collateral no longer covers the required margin, the protocol’s smart contract can liquidate the position, using the oracle price as its reference.