Sequencer

A sequencer is the component of a rollup that receives users' transactions, decides their order and produces the Layer 2 blocks that are later posted to the base chain. It is what gives rollups their fast confirmations, because the sequencer can accept a transaction in seconds rather than waiting for Layer 1. Most rollups today run a single sequencer operated by the development team, which introduces centralisation risks: it can go offline and halt the network, or reorder transactions for profit. Well-designed rollups mitigate this with forced-inclusion mechanisms that let users submit transactions directly to Layer 1 if the sequencer censors them, and with roadmaps toward shared or decentralised sequencing.