Data Availability
The assurance that the transaction data needed to verify a blockchain or layer 2 network can be accessed by anyone who needs it.
Data availability is the property that the raw data behind blockchain transactions is published and accessible enough for users, nodes, or validators to check the state of a network. In layer 2 systems, this usually means making sure the data needed to reconstruct balances and verify updates is not hidden by the operator or sequencer. It is different from execution: a rollup might process transactions off the main chain, but it still needs a reliable way to make the underlying data available for verification and dispute resolution.
It matters because users must be able to prove what happened if something goes wrong. For example, an optimistic rollup can post compressed transaction data to Ethereum so others can challenge invalid state updates. If the data were unavailable, watchers could not confirm whether the rollup’s state is correct, and users might struggle to exit safely. Some systems use the main chain for data availability, while others use separate data availability layers, trading off cost, security assumptions, and scalability.
Other terms in Layer 2 & Scaling
Fraud Proof
A fraud proof is evidence submitted to a blockchain to show that a proposed transaction result or rollup state is invalid.
Layer 2
A Layer 2 is a secondary network or protocol built on top of a blockchain to process transactions faster and cheaper while relying on the main chain for security.
Layer 3
A Layer 3 is an application-specific blockchain layer built on top of a Layer 2 to add customization, scalability, or specialized features.
Modular Blockchain
A blockchain design that splits core jobs like execution, settlement, consensus, and data availability across separate specialized layers.