Bundler

What is Bundler?

A bundler is a specialized node in the Account Abstraction (ERC-4337) ecosystem. Its job is to collect "User Operations" and package them into a single transaction to be sent to the blockchain.

How does Bundler work?

1. Users of "Smart Accounts" sign User Operations (UserOps) instead of standard transactions.
2. These UserOps are sent to a dedicated mempool for bundlers to see.
3. The bundler picks up multiple UserOps and "bundles" them together.
4. It submits this bundle as a single transaction to a "singleton" EntryPoint contract.
5. The bundler pays the gas for the transaction and is reimbursed by the users or a "paymaster."

Why does Bundler matter?

Bundlers enable the core features of Account Abstraction, such as gasless transactions and batched actions. They allow smart contracts to function as wallets without requiring changes to the underlying blockchain protocol.

Key features of Bundler

• Aggregator of User Operations
• Off-chain mempool participant
• Essential for ERC-4337 compatibility
• Facilitates gas abstraction (via Paymasters)
• Non-custodial (cannot change user's intent)

Examples of Bundler

• Pimlico and Alchemy, which provide high-performance bundler infrastructure.
• A wallet using a bundler to allow a user to "Approve" and "Swap" in one click.
• A game using a bundler to bundle multiple in-game actions into a single transaction.