Sequencer
The entity that orders transactions on a rollup — typically centralised today, with decentralisation roadmaps in progress.
A centralised sequencer can censor, reorder, or front-run transactions, but cannot steal funds outright (rollups inherit L1 settlement security). Sequencer downtime causes user-facing outages; sequencer decentralisation is a roadmap milestone for most major L2s.
Related terms
- RollupAn L2 architecture that batches transactions off-chain and posts compressed state + proofs back to L1 for settlement.
- Optimistic rollupAn L2 that posts state roots to L1 and assumes them valid unless a fraud proof is submitted within a challenge window.
- L2 (Layer-2)A scaling network that inherits security from an L1 by posting state roots back — rollups, validiums, plasma.
- MEV (maximal extractable value)Value an entity ordering transactions in a block can extract from rearranging, inserting, or censoring them.