---
title: Building Windows
description: Building Bun on Windows
---

This document describes the build process for Windows. If you run into problems, please join the [#contributing channel on our Discord](http://bun.com/discord) for help.

It is strongly recommended to use [PowerShell 7 (`pwsh.exe`)](https://learn.microsoft.com/en-us/powershell/scripting/install/installing-powershell-on-windows?view=powershell-7.4) instead of the default `powershell.exe`.

## Prerequisites

### Enable Scripts

By default, running unverified scripts are blocked.

```ps1
Set-ExecutionPolicy -Scope CurrentUser -ExecutionPolicy Unrestricted
```

### System Dependencies

Bun v1.1 or later. We use Bun to run it's own code generators.

```ps1
irm bun.sh/install.ps1 | iex
```

[Visual Studio](https://visualstudio.microsoft.com) with the "Desktop Development with C++" workload. While installing, make sure to install Git as well, if Git for Windows is not already installed.

Visual Studio can be installed graphically using the wizard or through WinGet:

```ps1
winget install "Visual Studio Community 2022" --override "--add Microsoft.VisualStudio.Workload.NativeDesktop Microsoft.VisualStudio.Component.Git " -s msstore
```

After Visual Studio, you need the following:

- LLVM 21.1.8
- Go
- Rust
- NASM
- Perl
- Ruby
- Node.js

<Note>The Zig compiler is automatically downloaded, installed, and updated by the building process.</Note>

Use [Scoop](https://scoop.sh) to install these remaining tools.

```ps1 Scoop (x64)
irm https://get.scoop.sh | iex
scoop install nodejs-lts go rust nasm ruby perl ccache
# scoop seems to be buggy if you install llvm and the rest at the same time
scoop install llvm@21.1.8
```

For Windows ARM64, download LLVM 21.1.8 directly from GitHub releases (first version with ARM64 Windows builds):

```ps1 ARM64
# Download and install LLVM for ARM64
Invoke-WebRequest -Uri "https://github.com/llvm/llvm-project/releases/download/llvmorg-21.1.8/LLVM-21.1.8-woa64.exe" -OutFile "$env:TEMP\LLVM-21.1.8-woa64.exe"
Start-Process -FilePath "$env:TEMP\LLVM-21.1.8-woa64.exe" -ArgumentList "/S" -Wait
```

<Note>
  Please do not use WinGet/other package manager for these, as you will likely install Strawberry Perl instead of a more
  minimal installation of Perl. Strawberry Perl includes many other utilities that get installed into `$Env:PATH` that
  will conflict with MSVC and break the build.
</Note>

If you intend on building WebKit locally (optional, x64 only), you should install these packages:

```ps1 Scoop
scoop install make cygwin python
```

<Note>Cygwin is not required for ARM64 builds as WebKit is provided as a pre-built binary.</Note>

From here on out, it is **expected you use a PowerShell Terminal with `.\scripts\vs-shell.ps1` sourced**. This script is available in the Bun repository and can be loaded by executing it:

```ps1
.\scripts\vs-shell.ps1
```

To verify, you can check for an MSVC-only command line such as `mt.exe`

```ps1
Get-Command mt
```

<Note>
  It is not recommended to install `ninja` / `cmake` into your global path, because you may run into a situation where
  you try to build bun without .\scripts\vs-shell.ps1 sourced.
</Note>

## Building

```ps1
bun run build

# after the initial `bun run build` you can use the following to build
ninja -Cbuild/debug
```

If this was successful, you should have a `bun-debug.exe` in the `build/debug` folder.

```ps1
.\build\debug\bun-debug.exe --revision
```

You should add this to `$Env:PATH`. The simplest way to do so is to open the start menu, type "Path", and then navigate the environment variables menu to add `C:\.....\bun\build\debug` to the user environment variable `PATH`. You should then restart your editor (if it does not update still, log out and log back in).

## Extra paths

- WebKit is extracted to `build/debug/cache/webkit/`
- Zig is extracted to `build/debug/cache/zig/bin/zig.exe`

## Tests

You can run the test suite either using `bun test <path>` or by using the wrapper script `bun node:test <path>`. The `bun node:test` command runs every test file in a separate instance of bun.exe, to prevent a crash in the test runner from stopping the entire suite.

```ps1
# Setup
bun i --cwd packages\bun-internal-test

# Run the entire test suite with reporter
# the package.json script "test" uses "build/debug/bun-debug.exe" by default
bun run test

# Run an individual test file:
bun-debug test node\fs
bun-debug test "C:\bun\test\js\bun\resolve\import-meta.test.js"
```

## Troubleshooting

### .rc file fails to build

`llvm-rc.exe` is odd. don't use it. use `rc.exe`, to do this make sure you are in a visual studio dev terminal, check `rc /?` to ensure it is `Microsoft Resource Compiler`

### failed to write output 'bun-debug.exe': permission denied

you cannot overwrite `bun-debug.exe` if it is already open. you likely have a running instance, maybe in the vscode debugger?
