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Documentation Index

Fetch the complete documentation index at: https://bun.com/docs/llms.txt

Use this file to discover all available pages before exploring further.

This document describes the build process for Windows. If you run into problems, please join the #contributing channel on our Discord for help. It is strongly recommended to use PowerShell 7 (pwsh.exe) instead of the default powershell.exe.

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Prerequisites

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Enable Scripts

By default, running unverified scripts are blocked. 
Set-ExecutionPolicy -Scope CurrentUser -ExecutionPolicy Unrestricted

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System Dependencies

Bun v1.1 or later. We use Bun to run it’s own code generators. 
irm bun.sh/install.ps1 | iex
Visual Studio 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: 
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
The Zig compiler is automatically downloaded, installed, and updated by the building process.
Use Scoop to install these remaining tools.
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):
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
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.
If you intend on building WebKit locally (optional, x64 only), you should install these packages:
Scoop
scoop install make cygwin python
Cygwin is not required for ARM64 builds as WebKit is provided as a pre-built binary.
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: 
.\scripts\vs-shell.ps1
To verify, you can check for an MSVC-only command line such as mt.exe 
Get-Command mt
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.

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Building

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. 
.\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).

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Extra paths

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

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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. 
# 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"

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Troubleshooting

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.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

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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?