What is a testnet? The blockchain testing ground explained

A testnet is a separate blockchain network that mirrors a production chain’s rules and functionality but uses tokens with no monetary value. It is where developers break things, test upgrades, and discover bugs before those bugs can cost anyone real money. Summary A testnet is a blockchain network that runs the same software as a mainnet but uses valueless tokens, allowing developers to test smart contracts, protocol upgrades, and applications without financial risk. Ethereum has run multiple testnets over its history, with Sepolia and Holesky serving as the primary public testing environments as of 2026 after the deprecation of Goerli. Testnet tokens are free and can be obtained from faucets, which are web services that distribute small amounts of test tokens to developer wallet addresses. Major protocol upgrades like Ethereum’s Pectra and Cardano’s van Rossem hard fork were deployed to testnets months before reaching mainnet, where they were tested under conditions designed to surface edge cases and failure modes. Testnets are not perfect replicas of mainnet conditions. They typically have fewer validators, lower transaction volume, and different economic incentives, which means ...