A validity-proof rollup submits a proof that a batch moves the system from an accepted prior state to a new state according to specified rules. A verifier on the settlement chain checks the proof and its public inputs. This can make checking a batch much cheaper than replaying all its execution there. The assurance is only as appropriate as the proved computation: a correct proof of incorrectly specified application rules does not repair those rules.

Imagine a batch containing many transfers. The operator computes the updated balances and a commitment to the resulting state, then produces a proof linking that result to the allowed transitions. The base-layer verifier accepts or rejects the claim. A user may see the transfer in a rollup interface before proof generation and settlement finish. Withdrawals still depend on proof publication, verification, base-layer finality, and the deployment's withdrawal process, even though they need not wait for an optimistic fraud-challenge window.

The name ZK rollup does not mean every user transaction is secret. Many systems publish enough data for outsiders to reconstruct state, while using proof technology principally to establish correctness. If a system keeps required data elsewhere, its availability assumptions differ and it may be classified as a validium. Evaluate the prover, verifier contracts, published data, upgrade keys, and escape mechanisms separately. A proof label alone does not establish private balances, unstoppable transaction inclusion, or the absence of privileged administrators.