What is a light client?
- Author
- CRYPTO PORT Editorial
- Published
- Updated
- Reading time
- 5 min
In short
A light client verifies what it needs from block headers and proofs instead of holding the whole chain. That makes it viable on a phone or an embedded device, but it verifies less than a full node and still depends on others to supply data.
Key points
- Verifies using headers and proofs rather than full blocks
- Runs on very little bandwidth and storage
- Cannot check every consensus rule, so some trust remains
- Also used to verify one chain from inside another
Definition
A client that keeps no full copy of the chain and instead verifies specific facts using block headers plus minimal proofs.
Bitcoin's original paper anticipated this as simplified payment verification. The client follows only block headers and checks membership of a transaction with a Merkle proof. A header is 80 bytes, so even the full set of them stays in the hundreds of megabytes.
The limits are equally clear. A light client does not itself check that every transaction in a block obeys the rules, so if a majority produced an invalid block it might accept it. A full node in the same situation rejects the block outright.
Ethereum added a design in which a rotating sync committee of validators signs headers, letting a light client verify them cheaply. The same machinery underpins bridges that verify one chain's state from inside another, without trusting a bridge operator's word.
Watch out for
- · A light client is not as independent as a full node and can accept an invalid block
- · With few peers, a hostile provider can withhold data and keep showing you a stale state
- · Most phone wallets are not even light clients — they simply query the vendor's servers