chainwork

Chainwork is a metric used in blockchain and distributed ledger systems to quantify the total amount of computational work expended to build a blockchain up to a given block. It serves as a measure of the cumulative effort behind a chain, and it underpins the chain selection process when competing forks arise. In essence, the chain with greater chainwork is considered more trustworthy under typical proof-of-work assumptions.

Calculation generally links chainwork to the work required to mine each block. In proof-of-work systems, the work contributed by a block is proportional to the inverse of its difficulty target. A common mathematical representation is that block work scales with 2^256 divided by the target, and chainwork is the sum of these work values along the chain. Modern implementations often store an abstract cumulative value, such as total difficulty, which increases as new blocks are added.

Role in consensus and fork resolution is central: when multiple chains exist, nodes prefer the chain with higher chainwork, aligning with the principle that the heaviest or longest chain represents the valid history. This helps limit reorganizations and provides resilience against transient forks.

Observability and limitations: Chainwork is typically internal data used by nodes and clients to compare chains rather than something shown directly to users. It is most relevant to proof-of-work networks; in other consensus models, the concept translates to analogous notions like total difficulty or chain weight. Limitations include dependence on the difficulty model and potential misinterpretation when comparing across differently parameterized networks.

See also: proof of work, total difficulty, longest-chain rule, blockchain.