# Merkle proof

> A compact cryptographic proof that one item belongs to a big set — verify a leaf against the root hash without holding the whole tree.

A Merkle tree hashes pairs of items upward until one root hash commits to the whole set. To prove item X is in it, you only need the few sibling hashes along X's path — a handful of hashes instead of the entire list. That is how a contract can verify 'this wallet is on the airdrop list' without storing ten thousand addresses.

It is the standard trick wherever on-chain storage is expensive: whitelists, state verification, light clients, certificate transparency. The pattern to remember — commit a small hash on-chain, keep the big data anywhere — is the same one behind most 'verify off-chain data on-chain' designs.

## Related terms

- https://dfieldsolutions.com/en/glossary/on-chain.md
- https://dfieldsolutions.com/en/glossary/smart-contract.md
- https://dfieldsolutions.com/en/glossary/spl-token.md

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Source: https://dfieldsolutions.com/en/glossary/merkle-proof
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