Tendermint consensus

Tendermint is a Byzantine-fault-tolerant consensus engine, descended from PBFT, that powers the Cosmos ecosystem (the implementation is now called CometBFT). It fuses classical BFT voting with proof of stake: a validator's vote is weighted by the amount of stake bonded to it, and the protocol tolerates faulty validators controlling up to one-third of the total stake. Its signature property is instant, single-block finality — when a block commits, it is final immediately, with no fork-choice rule and no waiting for confirmations.

Consensus proceeds in heights (one block each), and within a height in rounds, each with a deterministic proposer chosen in weighted round-robin. A round has three steps: propose, where the proposer broadcasts a block; prevote, where validators broadcast a prevote for that block (or nil); and precommit, where seeing more than two-thirds of stake prevote a block lets a validator precommit it. Collecting more than two-thirds precommits commits the block. A locking mechanism ties a validator that precommits a block to keep prevoting it in later rounds unless it sees a newer two-thirds prevote, which prevents two different blocks from ever both gathering a supermajority at the same height.

This design deliberately favors safety (consistency) over liveness (availability). If more than one-third of stake is offline or Byzantine, no block can reach a two-thirds precommit and the chain simply halts rather than risk forking — the opposite trade-off from Nakamoto chains, which keep producing blocks but only offer probabilistic finality. Double-signing (precommitting two different blocks at the same height) is a cryptographically provable offense that gets the validator's stake slashed.