Testnet vs Mainnet

A testnet is a practice version of a blockchain where developers try out code using worthless tokens, while the mainnet is the real, live network where transactions carry actual value and finality. Knowing the difference matters because sending real funds to a testnet address (or vice versa) means losing them for good, since the two networks don't talk to each other. For example, Ethereum's Sepolia testnet lets developers test a new smart contract for free before deploying the same code to Ethereum mainnet, where a failed transaction can cost real ETH in gas fees. Projects often run for months on testnet, offering "testnet tokens" with no market value, before launching on mainnet with tokens people can actually buy, sell, or stake.