Testnet

Testnet is a parallel Bitcoin blockchain that lets developers and tinkerers experiment with transactions, wallets, and applications using coins that carry no real-world value. It shares Bitcoin's core protocol but relaxes some restrictions, so software can be exercised safely without risking real funds or destabilising the main network.

How testnet differs from mainnet

Testnet runs on its own ports (default P2P 18333, RPC 18332 versus mainnet's 8333/8332) and uses a distinct address prefix (0x6F instead of 0x00), so testnet coins and addresses cannot accidentally cross over to the real chain. It has its own genesis block and its own proof-of-work history. A node joins it with the -testnet flag or testnet=1 in the configuration file.

The 20-minute difficulty rule

To keep blocks flowing even when little hash power is present, testnet3 includes a special rule: if no block is found for 20 minutes, difficulty resets to the minimum for a single block, then returns to its prior value. This convenience also enabled timestamp-warping abuse that produced erratic block storms, which is why testnet4 (added in Bitcoin Core v28.0) tightened the rules.

Because mined testnet coins still require maturing, the same 100-block waiting period applies before a reward can be spent. For more reliable, signed alternatives see Signet and Regtest, and grab free coins from a Bitcoin faucet.