A blockchain oracle delivers external or computed data to smart contracts. DeFi applications use oracle feeds for values such as asset prices, reserves, interest rates, and layer-2 sequencer status.
The data pipeline matters
A feed can depend on market data sources, node operators, aggregation rules, update thresholds, proxy contracts, and governance. Decentralizing one layer does not remove every dependency.
Blockchains cannot verify outside facts by themselves
A smart contract can verify onchain state, but market prices and other external facts must enter through a data process with its own assumptions and operators.
Applications must check freshness and limits
A contract should consider when a value was last updated and whether it falls within reasonable bounds. Delays, outages, extreme volatility, or thin markets can make an otherwise valid feed unsuitable for an action.
The consuming application needs safeguards
Applications should check timestamps, deviations, feed addresses, network conditions, and fallback behavior rather than blindly accepting the latest returned number.
Sources
Educational information, not investment advice.