# ERC 4337: What is the bundler 

By [B+](https://paragraph.com/@b-2) · 2023-03-15

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TLDr: Bundler: receives `UserOperations` via a JSON RPC Client and submits them to the `EntryPoint`

![](https://storage.googleapis.com/papyrus_images/4d0520330cf0dfb42c722838dc2ea9e8d76d30447fae090192e879e7d4729787.png)

### The steps are:

1.  The user submits a transaction as `UserOperation` via the JSON Rpc client
    
2.  The `UserOperation` will send to the Mempool
    
3.  ExecutionManager will fetch the `UserOperation` from `mempool` and package submitted to the smart contract call: `Entrypoint`
    
4.  The `EventManager` will subscript to any event that sends from the `Entrypoint` and update the UserOperation based on the event

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*Originally published on [B+](https://paragraph.com/@b-2/erc-4337-what-is-the-bundler)*