What Is a Testnet in Crypto?

A testnet is a practice copy of a blockchain, running the same software as the real network but with coins that are free and deliberately worthless. It exists so that developers — and curious beginners — can send transactions, deploy code and make mistakes without losing anything. Ethereum's main practice networks today are called Sepolia and Hoodi.

Why can't developers just test on the real network?

Because on the live network every experiment costs real fees and every bug can cost users real money. A blockchain is also permanent: there is no undo button, and no support desk to reverse a bad transaction. So the testnet is a flight simulator. A pilot can crash it on a Tuesday afternoon, learn something, and walk away, which is exactly what you want before anyone real gets on the plane. Bitcoin has had one since the early days, and Ethereum apps are usually tested on Sepolia before they ever touch Ethereum proper.

Where do testnet coins come from?

From a faucet: a free website that drips a small amount of test coins into any address that asks. That is the entire supply mechanism, and it is why test coins have no market. They are printed on demand by whoever runs the faucet.

Is a testnet permanent?

No, and that is a useful difference. Test networks are retired and replaced when they get too big or too tangled to maintain; Ethereum shut one of its older ones down in September 2025 and moved everyone across. Nothing of value was lost, because nothing on a testnet is meant to have value in the first place.

Here is a genuinely worthwhile hour: open MetaMask, switch the network to Sepolia, take some free coins from a faucet, and practise sending, swapping and reading your transaction on a block explorer. You will learn more than any article can teach, and it cannot cost you anything. One warning: nobody legitimately sells testnet coins. Anyone offering to buy or sell them is running a scam.