---
title: "builder"
description: "The Base block builder binary for flashblock production and block building."
source: https://basehub.org/binaries/builder/
---
import { LinkCard } from '@astrojs/starlight/components';

`base-builder` produces flashblocks every 200 milliseconds and assembles the sealed canonical blocks for Base. It orchestrates the build pipeline through `FlashblocksServiceBuilder`.

## Package

- **Crate name:** `base-builder-bin`
- **Binary name:** `base-builder`
- **Source:** [`bin/builder`](https://github.com/base/base/tree/main/bin/builder)
- **Dockerfile:** `etc/docker/Dockerfile.builder`

## Architecture

The builder binary bootstraps using `FlashblocksServiceBuilder`, which wires together:

1. **Block building** — Assembles transactions from the pool into execution payloads
2. **Flashblock production** — Produces 200ms sub-block preconfirmations streamed to subscribers
3. **Metering** — Tracks gas usage and resource consumption via `MeteringStoreExtension`
4. **Transaction pool RPC** — Exposes custom pool methods via `TxPoolRpcExtension`

The builder uses jemalloc as its global allocator for improved memory allocation performance.

## Key Extensions

| Extension | Purpose |
|-----------|---------|
| `FlashblocksServiceBuilder` | Orchestrates the full flashblocks pipeline |
| `MeteringStoreExtension` | Resource metering data store |
| `TxPoolRpcExtension` | Transaction pool RPC methods |

## Key Dependencies

- `base-cli-utils` — CLI utilities (logging, metrics)
- `base-builder-core` — Core block building logic
- `base-builder-metering` — Resource metering
- `base-builder-publish` — Block publishing and streaming
- `reth-optimism-node` — Reth node builder
- `jemalloc` — Memory allocator

## Build

```bash
# Build the builder binary
cargo build --bin base-builder --release
```

## Docker

```bash
# Build the image
docker build -t base-builder -f etc/docker/Dockerfile.builder .

# Run
docker run -it --rm base-builder [OPTIONS]
```

## Usage

```bash
./target/release/base-builder [OPTIONS]
```

## Source

<LinkCard title="View source on GitHub" href="https://github.com/base/base/tree/main/bin/builder" />