GRANDPA/BABE Algorithm | cryptocurrencies, blockchains & live prices

GRANDPA/BABE is the hybrid consensus mechanism used by Polkadot and Substrate-based blockchains, combining two separate protocols: BABE (Blind Assignment for Blockchain Extension) for block production and GRANDPA (GHOST-based Recursive Ancestor Deriving Prefix Agreement) for finality. BABE is a slot-based block production mechanism where validators are assigned to slots using a verifiable random function (VRF), with the probability of selection proportional to their stake. Multiple validators may be assigned to the same slot, in which case the network resolves the fork using a fork-choice rule. GRANDPA operates as a finality gadget that runs alongside BABE, voting on chains rather than individual blocks — it can finalize multiple blocks at once by voting on the highest block that two-thirds of validators agree on.

The separation of block production and finality provides strong guarantees: BABE ensures new blocks are always being produced (liveness), while GRANDPA ensures finalized blocks are irreversible (safety). GRANDPA can finalize hundreds of blocks in a single round when the network is operating smoothly, providing finality in approximately 12-15 seconds under normal conditions. If GRANDPA stalls due to network issues, BABE continues producing blocks, and GRANDPA can catch up by finalizing all accumulated blocks once it resumes. The protocol tolerates up to one-third Byzantine validators for both safety and liveness. GRANDPA's chain-voting approach is more efficient than block-by-block finality protocols because a single vote can finalize an entire chain prefix.

GRANDPA/BABE powers the Polkadot relay chain and its ecosystem of parachains, as well as Kusama (Polkadot's canary network) and numerous other Substrate-based blockchains. Polkadot was created by Gavin Wood, co-founder of Ethereum, and developed by Parity Technologies and the Web3 Foundation. The consensus mechanism is a core part of the Substrate framework, making it available to any project building with Substrate. The protocol was designed with Polkadot's multi-chain architecture in mind, where the relay chain provides shared security to connected parachains, each of which can have their own block production logic while inheriting finality from GRANDPA on the relay chain.