What is data availability?

Data availability means the data needed to verify a block or state update and reconstruct the relevant state can be accessed. Seeing a commitment to data is different from being able to obtain the data itself.

Correct computation is a separate question. A validity proof can establish that a computation follows specified rules; users being able to obtain data for their own checks is another condition. Availability also does not promise that the same service will archive the data forever.

Example

Imagine a rollup publishing a commitment to new balances after processing hundreds of transactions. The commitment alone does not provide enough information to recalculate which transaction changed each balance. An observer can reconstruct the state if the required transaction data is accessible. Knowing only the commitment does not provide the same ability when data is withheld.

For a scaling network, publishing data to Ethereum introduces different assumptions from relying on an external network or a permissioned committee. Examine who can obtain the required data and under what conditions, as well as the data layer's name.

The rollup selection guide offers practical checks that place data availability alongside proof verification, withdrawals and contract upgrade authority.