In one sentence
A validator is a participant in a proof-of-stake network who has locked a deposit and, in exchange, may propose blocks and must vote on which blocks are correct.
How it works
On Ethereum, a validator is not a machine or a person but an identity: a signing key linked to a deposit. Whoever operates it runs validator software alongside a full node, which keeps it informed about the chain.
A validator has regular duties. Once in every epoch of 32 slots, it publishes an attestation — a signed vote on the current head of the chain and on the latest checkpoints. Occasionally, when chosen for a slot, it proposes a block. From time to time it is also picked for a sync committee of 512 validators, serving for about 27 hours, whose signatures help light clients follow the chain.
Rewards and penalties are designed to be predictable. Doing duties on time adds a little to the validator's balance. Missing them takes away roughly what would have been added. Only provable misbehaviour, such as signing two conflicting blocks or contradictory votes, leads to slashing and forced exit. Votes are signed with BLS signatures, which can be merged so that thousands of votes are checked almost as quickly as one.
One operator can run many validators, each with its own key and its own deposit. Validators can leave through an exit queue. Withdrawals of deposits became possible with an upgrade in April 2023.
A simple example
A validator's computer loses its internet connection for a day. It misses its attestations and its balance shrinks by roughly what it would otherwise have gained — no slashing, because being offline is not cheating. When it reconnects, it simply resumes its duties.
Common misconception
Misconception: Validators can freeze or take users' funds.
In fact: Validators cannot create signatures for addresses they do not control, so they cannot move anyone else's units. What they can do is choose which valid transactions go into the blocks they propose, which is why spreading validation across many independent operators matters.
Where you meet it
- Ethereum's consensus layer and other proof-of-stake networks.
- Block explorers that show who proposed each block.
- Debates about how concentrated block production is.
- Reports of slashing, which is rare and always publicly visible on the chain.
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.