Consensus (consensus rules)

In Bitcoin, consensus means that all nodesGlossaryNodeA computer that runs Bitcoin software and exchanges transactions and blocks with other nodes. Together, the nodes form the Bitcoin network; full nodes check every rule themselves.On the learning path: Stage 1 · Step 3 – How does Bitcoin work? →In the glossary →× independently reach the same result on which transactions are valid and which chain counts – without a vote and without a central authority.

How it works

• Fixed rules: every node checks every block itself – no double spending, valid signatures, no excessive block reward. Invalid blocks are rejected, no matter how much computing power is behind them.
• Most work wins: if there are briefly two valid chains, nodes follow the one with the most accumulated work (proof of workGlossaryProof of workThe method by which miners prove that they have done real computing work for a new block. It lets the network agree on the valid chain without a central authority, and makes rewriting old blocks extremely expensive.On the learning path: Stage 1 · Step 3 – How does Bitcoin work? →In the glossary →×).^[1]

Rule changes are called a soft forkGlossarySoft forkA change to the consensus rules that only tightens them. Blocks that follow the new rules remain valid for old nodes – so Bitcoin can be developed further without a chain split, as with SegWit and Taproot.In the glossary →× or a hard forkGlossaryHard forkA change to the consensus rules that allows previously invalid blocks. Old nodes reject such blocks; if not everyone goes along, two permanently separate chains emerge – and with them a new, separate currency.In the glossary →×.

Two examples

• 15 August 2010: a bug let a transaction in one block create around 184 billion BTC. Within five hours, a corrected version of the software was out; the chain without those coins prevailed.^[2]
• August 2026: a minority of nodes enforcing stricter rules (BIP 110) split off. In about eight hours, their chain found two blocks; by then the main chain was 48 blocks ahead.^[3]

What this means for you

Neither miners nor developers nor a group of nodes can change the rules for everyone on their own. Anyone who enforces new rules that the rest of the network doesn’t follow ends up on a separate chain with its own currency. With your own full nodeGlossaryFull nodeA node that checks every block and every transaction itself against all the consensus rules. If you run a full node, you don’t have to trust anyone to know whether a payment is valid.In the glossary →×, you check for yourself. More in Forks & controversies.