# Validity Proof

> A cryptographic proof that a batch of transactions on a ZK-rollup followed all the rules.

Canonical URL: https://fudfomo.co/glossary/validity-proof
Source: What The Block! Dictionary v1.0 (last updated 2026-04-25), browsable at https://wtb.fudfomo.co.

## Definition

A validity proof is a small piece of cryptography attached to each batch on a ZK-rollup. It mathematically demonstrates that every transaction in the batch was valid, without the verifier having to re-run any of them.

Because the proof is checked instantly, there is no challenge window and withdrawals can settle quickly. Generating these proofs is computationally heavy, which is why ZK-rollups invest in specialised hardware and proof systems.

## Related terms

- [ZK-Rollup](https://fudfomo.co/glossary/zk-rollup): A layer 2 that posts cryptographic proofs back to the main chain to show its batches are valid.
- [Rollup](https://fudfomo.co/glossary/rollup): A type of layer 2 that bundles many transactions together and writes a summary back to the main chain.
- [Layer 2](https://fudfomo.co/glossary/layer-2): A faster, cheaper network built on top of a layer 1 like Ethereum. Borrows the main chain's security.

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