What is a blockchain node, and why run one?
A node is a computer that runs a blockchain's software and connects to other nodes.1 Full nodes keep a copy of the blockchain and check every block against the rules, so no single company holds the only record.2,3
A network of copies
A blockchain is a shared database, updated and kept by many computers in a network.4 Each of those computers is a node.2 On Ethereum, a node is any computer running Ethereum's software and connected to other computers doing the same.1 Ethereum's network is made up of thousands of independent nodes around the world.5
In Bitcoin's original design, new transactions are sent to all nodes. A node that makes a new block sends that block to all nodes too.6 Because the record is spread across many nodes, there is no single central point to attack.2 If one node misses a security update, only that node is affected.2
Kinds of node
| Kind | What it does |
|---|---|
| Full node | Stores the blockchain and checks that transactions are valid2 |
| Publishing node | A full node that also creates new blocks2 |
| Light node | Doesn't keep a full copy; downloads block headers and asks full nodes for the rest2,1 |
| Archive node | On Ethereum, a full node that keeps all history and never deletes old data1 |
Publishing nodes are called miners on proof-of-work blockchains and validators on proof-of-stake blockchains.2,7 The next two lessons explain both.
What full nodes check
A full node fully checks transactions and blocks.3 Almost all full nodes also pass valid transactions and blocks on to other full nodes.3 A node accepts a block only if every transaction in it is valid and its coins have not already been spent.6
Full nodes enforce the rules, so they can't be tricked into accepting blocks that break them.1 If every node were a light node, the nodes that make blocks could attack the network.1
Don't trust, verify
Running your own node lets you check the data yourself, instead of trusting someone else's computer.1 "Don't trust, verify" is a popular saying in the blockchain world.1 Most Bitcoin wallets don't work this way. They are lightweight apps that don't download the whole blockchain.8
Running a node has costs. Bitcoin.org says a new Bitcoin full node downloads around 740 gigabytes the first time it starts.3 An Ethereum node has to run two programs, called clients: an execution client and a consensus client.1
Many teams, one set of rules
Ethereum's clients are written by different teams in different programming languages.1 They all follow one shared specification.1 Having several clients reduces the network's dependence on one piece of code, so a single bug is less likely to bring everything down.1
- Nodes and clients. ethereum.org developer docs, page updated 13 July 2026.
- NIST IR 8202: Blockchain Technology Overview. US National Institute of Standards and Technology (Yaga, Mell, Roby, Scarfone), October 2018.
- Running a full node. Bitcoin Project, bitcoin.org.
- Intro to Ethereum. ethereum.org, page updated 22 April 2026.
- What is Ethereum?. ethereum.org, page updated 31 March 2025.
- Bitcoin: A Peer-to-Peer Electronic Cash System. Satoshi Nakamoto (whitepaper, hosted at bitcoin.org), 2008.
- The Merge. ethereum.org, page updated 15 May 2026.
- Frequently Asked Questions. Bitcoin Project, bitcoin.org.
General education built from the publicly available sources listed above. Not financial, legal, tax or investment advice. Naming a company, project or regulator is not an endorsement either way. Last checked 2026-10-22. Terms and disclaimer.