Introduction to Oracles

Blockchains execute code deterministically: every node replays the same transactions and reaches the same state. That isolation is a security feature, but it also means a smart contract cannot natively ask a website for today's ETH price, a weather API for rainfall, or a bank for an account balance.

Oracles are the middleware that brings off-chain facts on chain in a form contracts can read. They do not replace consensus — they supply inputs that consensus-driven logic can act on. Lending protocols, derivatives, insurance, gaming, and real-world asset rails all depend on that bridge.

This course walks through why oracles exist, how major networks like Chainlink work, where they fail, and how to integrate feeds without becoming the next headline exploit. Oracle quality is infrastructure — treat it with the same seriousness as your contract audits.