Day 16 — How Can a Blockchain Know What Happened Outside It?

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Why blockchains need oracles

A blockchain oracle brings outside information to a blockchain. Smart contracts need this because they cannot freely browse the web.

That limitation is intentional. Every node must be able to reach the same result.

If each node fetched a website on its own, the answers could differ. Then the network could not agree.

Smart contracts can verify on-chain data easily. However, real-world facts live outside the chain.

For example, a lending app may need the price of ether. A prediction market may need a sports result. An insurance contract may need weather data.

An oracle delivers that information in a form the contract can use.

An oracle can become a weak point. If it reports a bad price, a contract may make a bad decision.

Because of that, many oracle systems use several data sources. Some also use multiple operators.

This reduces risk, but it does not remove risk completely.

Imagine a smart contract that lends stablecoins against ether. It must know the current ether price.

The oracle supplies that price. Then the contract can decide whether a loan is safe.

A blockchain oracle is a bridge between on-chain code and outside facts. It is useful, but it must be designed carefully.