A bundler is the infrastructure that makes ERC-4337 work. Smart accounts do not send normal transactions; they produce UserOperations. The bundler collects those, checks them, packs several into one transaction to the EntryPoint contract and pays the gas up front, after which it is reimbursed by the accounts or their paymasters.
What a Bundler Does
- Accepts UserOperations through a standard JSON-RPC API, including gas estimation for the wallet.
- Simulates validation of each operation and enforces the ERC-4337 validation rules, so one bad operation cannot make the whole bundle fail.
- Tracks reputation of accounts, factories and paymasters, and throttles entities that cause failures.
- Builds and submits bundles with a gas price strategy that gets them included without overpaying.
- Handles failures: replaced transactions, reorgs and operations that become invalid while waiting.
Use a Provider or Run Your Own?
Hosted bundlers from providers such as Alchemy, Pimlico, Biconomy and others are the fastest way to start and work well for most applications. We integrate them, often with a second provider as fallback. Running your own bundler makes sense when you need a chain no provider supports, full control over ordering and uptime, private flows that should not touch a public mempool, or lower costs at high volume. We set up and operate self-hosted bundlers based on established open-source implementations, with monitoring and alerting.
What We Watch For
- Matching EntryPoint versions across accounts, bundler and paymaster.
- Accurate gas estimation, including layer 2 data costs.
- Funding of the bundler's own wallet, with alerts before it runs low.
- Latency from submission to inclusion, measured per chain.
Want users to transact without holding gas? See gasless transactions for every method, from paymaster sponsorship and EIP-7702 to relayers and permit signatures. For signing see EIP-712.
Frequently Asked Questions
Do we need our own bundler?
Usually not at the start. A hosted bundler with a fallback is enough for most products; self-hosting pays off with specific chains, control or volume.
How does the bundler get paid?
The EntryPoint reimburses the bundler from the smart account's deposit or the paymaster's deposit, as part of the same transaction.
Can a bundler steal funds?
No. It can only submit operations the accounts have signed. It could delay or censor them, which is why a fallback provider matters.
Who owns the code?
Ownership of the source code is set out in the contract, and the code can be fully yours, including documentation and tests.
Part of our account abstraction work.
Set Up Reliable Bundling
Tell us your chains and expected volume. We will choose, integrate or run the bundler setup that keeps your users' operations flowing.