// GLOSSARY -- WEB3 INFRASTRUCTURE

What is Bundler?

1 min read Updated

A bundler in account abstraction (ERC-4337) is a service that collects UserOperations from users, bundles them into a single transaction, and submits them to the blockchain — analogous to block builders for regular transactions.

WHY IT MATTERS

Bundlers are the transaction submission layer of ERC-4337 account abstraction. Users create UserOperations (intents describing desired on-chain actions) and send them to bundlers. Bundlers validate, simulate, and submit these operations to the EntryPoint contract.

Bundlers can optimize: batching multiple UserOperations for gas efficiency, ordering for MEV extraction, and validating against the EntryPoint contract to avoid reverts.

Major bundler implementations include: Pimlico, Biconomy, Stackup, and Alchemy. The bundler market is competitive and increasingly commoditized.

FREQUENTLY ASKED QUESTIONS

Why do we need bundlers?
ERC-4337 UserOperations can't be submitted directly to the blockchain — they need to be wrapped in regular transactions. Bundlers handle this, similar to how validators include regular transactions in blocks.
Are bundlers centralized?
Currently, most applications use specific bundler services. But anyone can run a bundler — the protocol is permissionless. Over time, the bundler market should decentralize through competition.
What is the bundler mempool?
A separate mempool for UserOperations, distinct from the regular transaction mempool. Bundlers collect UserOps from this pool, validate them, and include them in bundles.

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