A full node is a computer running blockchain client software that downloads every block and checks every transaction in it against the network's consensus rules for itself. It keeps an up-to-date copy of the current state, such as Bitcoin's set of unspent outputs or Ethereum's account balances, relays valid transactions and blocks to its peers, and refuses anything that breaks the rules, no matter who produced it.
Full nodes are one kind of node; the wider family, including light, pruned, archive, mining and validator nodes, is set out in Different Types of Blockchain Nodes. Running a full node does not require mining or staking and earns no reward. Its value is independence: a user who runs one does not have to trust an exchange, a wallet provider or a block explorer to tell them which transactions are valid.
Full node in plain terms
Imagine a club that keeps its accounts in a shared ledger. Most members simply ask the treasurer what their balance is. A few members keep their own complete copy of the ledger and re-add every entry themselves each time a new page arrives. If the treasurer ever slips in a mistake or a made-up payment, those members notice at once and refuse to accept the page.
A full node is one of those careful members. It does not take anyone's word for the state of the accounts. It checks every page from the very first one, and because many people do the same, nobody can quietly change the rules.
How a full node works
When a new full node starts, it connects to peers and performs an initial block download, fetching the chain from the genesis block onward and verifying each block in turn: the proof of work or validator signatures, every digital signature, that no coin is spent twice, and that no more coins are created than the protocol allows. Once synchronised, it repeats those checks on each new block and keeps a mempool of valid unconfirmed transactions to pass on.
On Bitcoin a full node is a single program, most commonly Bitcoin Core. Since the Merge in 2022, an Ethereum full node runs two paired programs: an execution client, which processes transactions and smart contracts, and a consensus client, which follows proof-of-stake block agreement. A staking validator is a full node plus validator software and staked ether.
Full, pruned, archive and light nodes
| Node type | Validates everything itself | Keeps |
|---|---|---|
| Full node | Yes | Current state plus the blocks it has stored |
| Pruned node | Yes | Current state and only recent blocks; Bitcoin Core lets users cap block storage, with a minimum of 550 MiB |
| Archive node | Yes | Every historical state, so any past balance can be queried directly; mostly used by explorers and data providers |
| Light client | No | Block headers only; relies on full nodes for transaction data |
The light-client approach goes back to section 8 of Satoshi Nakamoto's Bitcoin whitepaper, which described simplified payment verification (SPV): checking that a transaction is included in a block using only the block headers and a Merkle proof. It is far cheaper but trusts that the longest chain follows the rules.
Reasons to run a full node
- Self-verification. A wallet connected to the user's own node confirms incoming payments without trusting anyone else, which matters to merchants and to holders using a non-custodial wallet.
- Privacy. Querying someone else's server reveals which addresses belong to the user; a personal node keeps that information local.
- Rule enforcement. Nodes decide which blocks they accept. In Bitcoin's 2017 SegWit dispute, the threat that node operators would enforce a soft fork themselves helped push miners to activate it.
- Infrastructure. Exchanges, custodians, the Lightning Network and block explorers all depend on full nodes they operate.
Costs and decentralisation
A full node needs steady bandwidth, a reliable disk and the time to sync, which can take from hours to days depending on hardware. The Bitcoin chain runs to hundreds of gigabytes, and an Ethereum full node needs a fast solid-state drive; exact figures change as the chains grow, so the client projects' own documentation is the best guide. Bitcoin's community has resisted larger blocks partly to keep these costs within reach of ordinary users, an argument at the heart of the dispute that produced Bitcoin Cash (BCH).
The number and spread of full nodes is often used as a rough sign of decentralisation, alongside measures such as the Nakamoto coefficient. Critics point out that node counts are easy to inflate and that most users still rely on hosted services, so independent verification remains the exception rather than the norm. Professional node operators and hosted node providers fill much of that gap, at the cost of concentrating trust.