Block Chain - Proposer–Builder Separation (PBS)

Proposer–Builder Separation is a blockchain design approach that separates the role of creating blocks from the role of proposing them to the network. This separation is mainly introduced to reduce harmful MEV and improve fairness in transaction ordering.

Why PBS Was Introduced
In traditional designs, the same entity both builds and proposes blocks. This gives them full control over transaction ordering and MEV extraction. PBS limits this power by splitting responsibilities, reducing incentives for manipulation and centralization.

Role of the Block Builder
Block builders collect transactions and construct optimized blocks, often aiming to maximize value. They focus on ordering transactions efficiently and may compete with each other to build the best possible block. Builders do not decide which block gets finalized.

Role of the Proposer
The proposer selects one of the blocks built by builders and proposes it to the network. The proposer does not reorder transactions inside the block, which limits direct MEV extraction. Their main task is to choose a valid block and submit it for consensus.

How PBS Works Conceptually
Builders submit block candidates to proposers. The proposer chooses a block based on predefined rules, often economic incentives. The chosen block is then validated and added to the blockchain through the consensus process.

Benefits of PBS
PBS improves fairness, reduces harmful MEV, and lowers the barrier to participation for validators. It also allows specialized block builders to compete, increasing efficiency while keeping proposers simpler and more decentralized.

Why PBS Is Important
Proposer–Builder Separation is a key innovation for modern blockchain scalability and security. It helps balance performance, decentralization and economic fairness, making blockchains more resilient as transaction volume and complexity grow.