It receives P2P data, independently validates blocks and transactions under locally running rules, maintains chainstate and a mempool, and can include a wallet, GUI and RPC interface.
Bitcoin Core is MIT-licensed software implementing Bitcoin rules and network interfaces. No repository alone defines Bitcoin: operators choose the software and version they actually execute.
During initial block download the node checks proof of work, linkage, transactions, scripts and UTXO spends. Its chainstate is locally derived rather than copied as an account balance from a trusted server.
Consensus rules determine what may enter a valid chain. Mempool and relay policy add local rules for unconfirmed transactions, so a non-standard transaction can remain consensus-valid even when a node will not relay it.
The peer-to-peer layer obtains headers, blocks and transactions from multiple peers. Mempools are temporary and differ; the active chain is selected by cumulative work among fully validated candidates.
The node validates without any wallet. The optional wallet manages descriptors, keys, addresses and transaction construction; bitcoin-qt adds a GUI, bitcoind is the daemon and bitcoin-cli calls RPC.
The data directory holds configuration, blocks, chainstate and optional wallets. Pruning deletes old block and undo data after validation to save disk but limits historical queries; txindex and other indexes must match the use case.
JSON-RPC can inspect node state and, with enabled modules, control wallets and other sensitive actions. Never expose it openly to the internet: restrict binding and firewalls, authenticate safely and grant only necessary permissions.
Official binaries publish SHA-256 checksums and signatures from multiple builders. Verify trusted key fingerprints as well as files; Guix builds and attestations let independent parties reproduce outputs instead of trusting one distributor.
Anyone may contribute patches, testing and review. Maintainers can merge repository changes, but cannot remotely rewrite other people's node rules; consensus changes affect only operators who deploy compatible software.
Download from an official source, verify hashes and signatures, read release notes, back up wallets and test recovery. Monitor IBD, peers, chain height, pruning and indexes, disk, debug.log and RPC exposure before upgrading. Bitcoin Core — integration/staging repository · Bitcoin Core — transaction relay and mempool policy · Bitcoin Core — contributing and maintainer model · Bitcoin Core — installed files and components · Bitcoin Core — JSON-RPC interface · Bitcoin Core — release process · Bitcoin Core — bootstrappable Guix builds · Bitcoin Core — download and signature verification
For the clearest picture, read this entry together with Full Node, Consensus rules, BIP (Bitcoin Improvement Proposal), Bitcoin, Soft Fork, Mempool. The reverse links also lead from Soft Fork, BIP (Bitcoin Improvement Proposal), Consensus rules, Blocksize War.