# Sequencer

> The operator that orders transactions on a layer 2 before they are posted to the main chain.

Canonical URL: https://fudfomo.co/glossary/sequencer
Source: What The Block! Dictionary v1.0 (last updated 2026-04-25), browsable at https://wtb.fudfomo.co.

## Definition

A sequencer is the service that decides the order of transactions on a rollup. Most rollups currently use a single centralised sequencer run by the team that built the chain, which makes them fast but also a point of trust.

If a sequencer goes offline or censors transactions, users can usually fall back to forcing transactions through the layer 1, but it is slower. Many teams are working on decentralised sequencer designs to remove this single point of failure.

## Related terms

- [Rollup](https://fudfomo.co/glossary/rollup): A type of layer 2 that bundles many transactions together and writes a summary back to the main chain.
- [Layer 2](https://fudfomo.co/glossary/layer-2): A faster, cheaper network built on top of a layer 1 like Ethereum. Borrows the main chain's security.
- [MEV](https://fudfomo.co/glossary/mev): Extra profit that validators or specialised bots can earn by reordering or inserting transactions in a block.

## See the full catalogue

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