Port 8333 is the commonly used TCP port for Bitcoin mainnet peer-to-peer connections.
Bitcoin nodes use a peer-to-peer network to exchange transactions, blocks, and information about other reachable nodes. The conventional listening port for the main Bitcoin network is TCP port 8333, although node operators can configure different ports and network conditions may affect connectivity.
Bitcoin also has separate network environments. The public testnet traditionally uses port 18333, while Bitcoin’s regtest environment commonly uses port 18444. These alternatives let developers test software without risking mainnet funds or waiting for real-world network conditions.
A port number does not identify a blockchain address, wallet, or transaction. It is simply a networking endpoint used by software. Bitcoin’s peer-to-peer protocol also supports modern connection methods such as encrypted transport options, so the familiar port number is a convention rather than an unchangeable rule.