Propellerhead developer tools "Rack Extensions take all the good things about plugins and then marries it to all the good things about Reason."
Ernst Nathorst-Böös, CEO

Design it, code it, test it, ship it.

With Propellerhead's Rack Extension platform, developers can move faster from initial idea to finished product than ever before. Regardless of whether your skills lie in hardcore DSP coding or in creating beautiful samples, the Rack Extension platform has all the tools you'll need to develop stunning instruments and effects and bring them to market with minimum effort and maximum support.

The recently updated developer toolkit adds features and tools for developers to create even more advanced and great-looking instruments and effects. With the Instrument Development Toolkit, it's easier than ever to build advanced instrument Rack Extensions, even without prior coding experience.

Rack Extensions are full citizens of the Reason Rack, cross-platform compatible, copy-protected, future-proof, and easy to sell direct to Reason users in the Propellerhead Shop. How to become a developer.

Reason 9.2 with Rack Extension SDK 2.5

Reason 9.2 has been released to the public, which means developers are now free to ship Rack Extension products featuring sample loading and an array of UI features such as panels, array support in displays, modifier key-clicks in displays and context menus.

With these technologies deployed to a huge user base of Reason 9 owners, the scene is set for a new generation of great Rack Extension products.
Read more

"We've already transformed a few of our current products to Rack Extensions. The back panel on each device with the many CV options truly reveals the power of Reason and Rack Extensions. Our next release is a dedicated Rack Extension synthesizer." Rob Papen, synth pioneer

Rack Extensions at a glance Rack Extensions are plugin additions for the Reason Rack. Using a comprehensive development kit provided by Propellerhead Software, third party developers can create instrument and effect units to be used inside of Reason.

Write once. Release everywhere.

Rack Extensions are cross platform, and will continue to work in the next version of Reason, and the next after that. You focus on building cool products, not maintain code. The Rack Extension platform will be kept up to date with current operating systems, removing the need for developers to update their products.

Full Citizens of the Reason Rack

A Rack Extension lives inside the Reason Rack, like any other rack device. They are fully integrated in the Reason user experience and work seamlessly with the host application. Automation, undo, cables on the back and music hardware integration—it's all handled by Reason.

Develop What Matters

With the Rack Extension technology, we have taken care of the mundane household tasks, so that you can focus on what matters: your product idea. Leave it to us to take care of file handling, automation, undo, music hardware integration and more.

Your Products. Direct to Market.

Distribute your Rack Extensions in the Propellerhead Shop, direct to all your customers. Propellerhead takes care of downloads, updates, demo downloads, copy protection and credit card processing for you—the works!

"As a very small company with limited resources, we are able to focus our attention on new ideas without being encumbered with the details of supporting various operating systems and plugin formats." Kurt Kurasaki, Peff

Tools for the job

  • API and Code Library

    The SDK comes with a library of useful code for Rack Extension development, such as FFT, memory handling, undo, sandbox, routing and communication with the Rack Extension host.

  • Recon

    Recon is used to test and debug your Rack Extension project. It's a test bench version of Reason that lets you load and run your prototype Rack Extensions.

  • LLVM Compiler

    With the LLVM compiler, you compile your C++ code to bitcode that is used to build the Rack Extension. It's the compiled bitcode that is uploaded along with your Rack Extension's other resources to Propellerhead's automated build system.

  • Rack Extension Designer

    The Rack Extension Designer (RED) is where you lay out and preview your 3D graphical interface.

  • Parts Library

    As an alternative to creating your own GUI objects in 3D, more than 100 interface parts such as knobs, buttons, faders and display objects are supplied in the Parts Library. Each object can be customized to adjust properties such as color, texture, and more.

Turn content into instruments

If you're apt at building sample libraries but don't speak the language of DSP, the Instrument Development Toolkit is for you. The Rack Extension SDK comes complete with an advanced scriptable sample player with a powerful array of built-in effects and more to kick-start your development. It also helps to convert content created for existing sample-based products into a Rack Extension instrument.

Support from start to finish

Help is there when you need it. We are as eager as you to see your projects finished and will always be there to help you out.

  • Developer Community

    There is nothing like learning from your peers. As a Rack Extension developer you’re granted access to the Rack Extension developer forum — a lively and active community of developers. Check out the collection of stickies full of helpful tips to get started.

  • Testing

    Testing is of course essential to a quality product release. The developer section of the our web site gives you access to beta testing tools to help you distribute beta licenses to your testers.

  • Tutorials

    The SDK comes with ten written tutorials with code and scripting examples that will help you along the process from initial design to finished product.

  • Example Projects

    To dip your feet in the Rack Extension technology, we have supplied three straightforward example projects that will show how to create a simple instrument, a simple effect unit and a device with a custom display.

  • Propellerhead Support

    For help and assistance, we are always available to help you out. Our staff can help and guide you with issues related to development, administration or sales issues.

Beyond Rack Extensions

Aside from Rack Extensions, Propellerhead offer several de facto industry standard technologies for developers to use.


ReWire is system for streaming audio from one application to another. Pioneered in Propellerhead Software's ReBirth, it is now supported in every major DAW on the planet. The API, which is written in ANSI C, also has support for play positioning information, MIDI streaming and a toolkit for communication between the applications.


The REX file format allows for free manipulation of timing and feel within a sampled groove. A REX file contains the original audio of the loop, the slices you have applied in ReCycle, and any effects or processing you have added in ReCycle. REX files are also compressed, using a non-lossy compression technique to save some precious hard drive space. The REX format has been implanted in just about any DAW or software sampler out there.


Remote is a protocol for handling communication between control surfaces (MIDI keyboards, remote control devices, etc.) and software applications (e.g. Reason). It handles everything from delivering MIDI note data from a keyboard to the application to using knobs, faders and buttons on a control surface for tweaking synth parameters in the application, controlling transport, etc. Remote also supports two-way communication, in order to make use of motor faders, dynamic displays and LEDs.


NN-XT is the flagship sampler in the Reason Rack. A fully featured sampling instrument, it comes with everything needed to build rich and natural sounding sample patches. The NN-XT file format is open to third party developers to allow external applications to create NN-XT patches.

About Propellerhead

Formed in 1994, Propellerhead Software is a privately owned company based in Stockholm, Sweden. Renowned for its musician-centric approach, Propellerhead has created some of the world's most innovative music desktop software applications, mobile apps and technology standards. Musicians, producers and the media have praised Figure, Reason, ReCycle and ReBirth applications for being inspiring, great sounding and of impeccable quality. Technologies such as ReWire and the REX file format are de-facto industry standards, implemented in all major music software. Today, Propellerhead's products are used all over the world by hundreds of thousands of professionals and enthusiasts for all kinds of music making.

Ask us anything!

Got more questions? Ask us and we'll do our very best to help you out!

How to become a Propellerheads developer

1 Register your company

Sign up for a Propellerhead user account and register your company with us.

Create an account Register your company

2 Get the tools

We’ll review and approve your registration. Then download the SDK and get your creativity going

3 Build and submit your Rack Extension

Design, build, and test your Rack Extension. When it's ready, submit it for sale in our shop.

Who can sign up?

Anyone can register as a developer, but only companies can sell Rack Extensions or ReFills in the Propellerhead Shop. The requirements for selling products in our shop are:

  • You need a company with some sort of Tax ID, being a sole proprietor is sufficient as long as you are registered for VAT.
  • You need a website.
  • You need an email address where customer can get product support.

This means each developer will sign up for a user account and then apply to register a new company. If you don’t have a company yet, you can put your own name in the company name field.

If you want to be included in a previously registered company, send an email to that company and ask them to add you as a developer.

There are no costs involved. Propellerhead Software will administer the authorization, copyrights, logos, and trademarks. We’ll also provide technical support, free of charge.