Library · Crypto, word by word · Infrastructure and development
What is a sequencer?
A sequencer is the party on a layer 2 network that collects users' transactions, decides their order, executes them and posts them in batches to the main chain. Rollups commonly rely on one centrally run sequencer, which is why their transactions can confirm in seconds.
What it means for you
A sequencer can delay or refuse your transaction and decides where it lands in the order; if it goes offline, the rollup can stall. Rollups are designed to let users submit a transaction directly to the main-chain contract, which the sequencer must then include within a time limit. Check whether a rollup offers that route and how long it takes.
How it works
The sequencer, or operator, is the only entity allowed to produce layer 2 blocks and submit batches to the rollup's contract on Ethereum, which gives it control over transaction ordering. That control creates censorship risk: an operator can refuse to include transactions or go offline. The safeguard is forced inclusion: users can submit transactions to the rollup contract on layer 1 instead, and the sequencer must include them within a time limit to keep producing valid blocks. In some designs the role rotates among stakeholders, and research on decentralized sequencers looks at replacing the single operator altogether.
Sources: ethereum.org: Optimistic rollups, ethereum.org: Zero-knowledge rollups, SoK: Decentralized Sequencers for Rollups (arXiv:2310.03616) · checked 4 October 2026
Related words
Educational content, not financial advice. Written by hand and checked against the source named above. Something wrong? Tell us and we reply within two business days.