Fraud Proof
A fraud proof is evidence submitted to a blockchain to show that a proposed transaction result or rollup state is invalid.
A fraud proof is a mechanism used by some Layer 2 systems, especially optimistic rollups, to let anyone challenge an incorrect claim about what happened off-chain. These systems publish transaction data or state commitments to a base blockchain and assume they are valid unless challenged within a set time window. If a watcher finds that a rollup operator submitted a wrong state update, they can provide a fraud proof showing the exact step where the computation breaks the rules.
Fraud proofs matter because they help Layer 2 networks inherit security from the base chain without forcing every transaction to be fully re-executed on-chain. This keeps costs lower while still giving users a way to dispute invalid results. A practical comparison is a receipt dispute: a cashier’s total is accepted unless someone checks the items and proves the math is wrong. In an optimistic rollup, the “math” is the transaction execution, and the fraud proof is the evidence that makes the blockchain reject the bad result.
Other terms in Layer 2 & Scaling
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.
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.