VarFern helps developers automatically download, install, and activate the right versions of development tools for each project — directly from the terminal.
Define your environment once, commit it, and run fern — done.
What Is VarFern?
VarFern is a lightweight Windows developer utility designed to make switching between different development tools and versions fast, predictable, and project-specific.
Modern projects often depend on specific versions of tools such as Java, SBT, Sass, and other command-line utilities. Managing these versions manually is time-consuming and error-prone.
With VarFern, each project defines its required tools in a .varFern file. Running fern in the project directory handles the rest.
Switch between tool versions in seconds, not minutes.
Every project carries its own environment definition.
Missing tools are downloaded and installed automatically.
Commit .varFern and share your environment with the team.
Designed specifically for Windows-based development workflows.
Simple plain-text config. No complex tooling required.
Usage
VarFern reads a .varFern file from your project root. Place the file, run a single command, and your terminal session is configured.
Add a .varFern file to the root of your project and list the required tools and their versions.
The file is plain text — commit it so every team member benefits from the same environment configuration.
Open a terminal in the project directory and run fern. VarFern downloads missing tools and configures the session.
The correct tool versions are immediately available in your terminal session.
Example .varFern file
java:21
sbt:1.10.11
sassBasic usage
fernPreserve existing environment variables
fern -envTip: Use fern -env when you already have custom environment variables set in your session and want to keep them while adding VarFern-managed tool configuration on top.
In the example above, java:21 requests Java 21, sbt:1.10.11 requests SBT 1.10.11, and sass requests the default supported Sass version.
Supported Tools
The table below lists the applications currently managed by VarFern along with their supported versions.
| Application | Supported Versions | Notes |
|---|---|---|
| Java | To be defined | |
| SBT | To be defined | |
| Sass | To be defined | |
| Other tools | To be defined |
Installation
Run the command below in your PowerShell terminal to install VarFern automatically.
# PowerShell installation command will be added herePrefer to install manually? Download the latest VarFern release directly and follow the included setup instructions.
Download VarFernSupport
Need help with VarFern, have a question, or want to report an issue? Send us a message and we'll get back to you.
For faster support, include:
Your Windows version, VarFern version, the command you ran,
your .varFern file contents (if relevant),
and a short description of the issue.