What Is a Smart Contract? Simple Explanation of How It Works
A smart contract is a program on a blockchain that carries out its terms by itself, with no middleman. DeFi, NFTs and thousands of tokens run on them. Here's how it works and where the risks are.
What it is
A smart contract is a program written to a blockchain. It works on an "if-then" rule: if the money has arrived and the condition is met, the contract sends the tokens by itself. No one can quietly change its code or refuse to pay, because the rules are visible to everyone.
The best-known network with smart contracts is Ethereum. Solana, BNB Chain, TON and many others support them too.
A simple example
You want to swap one token for another without an exchange. You send your coins to a swap contract; it uses a formula to calculate how much you're owed and immediately sends the second token to your wallet. There's no middleman, but you pay a network fee (gas) for the execution.
Where they're used
- DeFi: swaps, loans, liquidity pools.
- Tokens: most coins on Ethereum and similar networks are smart contracts.
- NFTs: digital items with an ownership record.
Risks
- Bugs in the code. A contract does exactly what's written, bugs included. DeFi hacks are often tied to vulnerabilities.
- Scam contracts. Signing an "approval" for an unverified contract can give it access to your coins.
- A transaction can't be reversed.
How to spot a scam is covered in the article rug pull and in the lesson how to avoid scammers.
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- A smart contract is a program on a blockchain that follows an "if-then" rule.
- DeFi, tokens and NFTs run on them.
- The code can contain bugs, and transactions can't be reversed.
Frequently Asked Questions
Who writes smart contracts?
Project developers. On Ethereum, the Solidity language is used most often. Serious projects order a code audit before launch.
Does an audit mean a contract is safe?
No. An audit reduces risk but doesn't rule out bugs. Even audited contracts have been hacked.
Can a smart contract be changed after launch?
It depends on how it's built. Some are immutable; others have an upgrade function, and then it matters who controls it.
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