In one sentence
A node is any computer that runs a blockchain's software, keeps a copy of its data and exchanges new transactions and blocks with other nodes.
How it works
There is no central server behind a public blockchain. The network is its nodes: ordinary computers, in homes and data centres, each running compatible software and connected to a handful of others.
A full node downloads every block and checks every rule for itself. Are the signatures valid? Is any output spent twice? Is the block within the size limit? Does it create more new units than the rules allow? If anything fails, the full node rejects the block — no matter who produced it or how much computation went into it. This independent checking is what keeps block producers honest.
A light client takes a shortcut. It downloads only block headers and asks full nodes for proofs, such as Merkle branches, about the transactions it cares about. That makes it small enough for a phone, at the cost of trusting that the majority of block production follows the rules.
Some nodes play extra roles. Miners and validators are nodes that also produce blocks. On Ethereum, an archive node keeps every historical state, and since the switch to proof of stake every Ethereum node runs two programs side by side: an execution client and a consensus client.
A simple example
A block arrives that pays its producer twice the number of new units the protocol allows. Every full node runs its checks, sees the excess, and throws the block away. The producer spent real resources making it, but the block never becomes part of the chain those nodes follow. Rules are enforced by the people who check, not only by those who produce.
Common misconception
Misconception: Nodes and miners are the same thing.
In fact: Every miner or validator runs a node, but most nodes never produce a block. Their job is to verify and pass information on — and, by refusing invalid blocks, to hold producers to the rules.
Where you meet it
- Wallet software connects to nodes to read balances and broadcast transactions.
- Block explorers are, underneath, nodes with a website on top.
- Network statistics count reachable nodes, though nobody knows the exact total.
Related cards
Sources
This card explains a technical concept for general education. It is not a recommendation to acquire, sell or hold any crypto-asset, and it is not financial advice.