What is System Designer used for?

System Designer is a low-code environment for modeling a system with UML, generating classes and method skeletons, and running the result from the designer. It is a good fit for designing a domain model and generating code skeletons, and prototyping component-based systems.

Is System Designer open source?

Yes. System Designer is open source under the Apache-2.0 licence. Its source code is on GitHub at design-first/system-designer.

Is System Designer free?

Yes. System Designer is open source, so the software itself is free to use.

What are some alternatives to System Designer?

Similar open-source tools in the Developer Tools category include Sponge, Visual Studio Code and code-server. SaaS products in the same category include WebStorm, Angular Material Blocks and Artiforge.

Is System Designer actively maintained?

The most recent commit to System Designer was on 7 January 2026, and the latest release is v5.4.0, published on 7 January 2026. The project has 1.1k stars on GitHub.

System Designer: open-source developer tools

About System Designer

System Designer, from Design First, is a low-code platform for creating systems rather than just applications. Its premise is that the most important part of software is the model, and it helps you define that model and generate the classes and components needed to build the system. A system, in its terms, is defined by a model, composed of components and reacts to events through behaviors. It is aimed at developers who like a model-first approach.

Models are drawn with UML and stored in a JSON format called MSON, which supports types, classes, one-to-one and one-to-many relationships, and multiple inheritance. After you create the model, the tool generates skeletons for your methods and you add the code that implements the behavior. Components can be created graphically, in the way you would create documents in a NoSQL database, with the tool acting as an object-document mapper.

You can run the system directly from the designer and export it, with HTML and JSON among the formats. The project is written in JavaScript and HTML and is licensed under Apache-2.0.

Key features

UML-based system modeling
Models stored in MSON JSON format
Generated method skeletons
Graphical component creation
Run the system from the designer
Export to HTML and JSON

Good fit for

→Designing a domain model and generating code skeletons
→Prototyping component-based systems

Built with: HTML; JavaScript
Tags: low-code; uml; modeling; code-generation; javascript; ide; metamodel; components

System Designer: questions and answers

What is System Designer used for?: System Designer is a low-code environment for modeling a system with UML, generating classes and method skeletons, and running the result from the designer. It is a good fit for designing a domain model and generating code skeletons, and prototyping component-based systems.
Is System Designer open source?: Yes. System Designer is open source under the Apache-2.0 licence. Its source code is on GitHub at design-first/system-designer.
Is System Designer free?: Yes. System Designer is open source, so the software itself is free to use.
What are some alternatives to System Designer?: Similar open-source tools in the Developer Tools category include Sponge, Visual Studio Code and code-server. SaaS products in the same category include WebStorm, Angular Material Blocks and Artiforge.
Is System Designer actively maintained?: The most recent commit to System Designer was on 7 January 2026, and the latest release is v5.4.0, published on 7 January 2026. The project has 1.1k stars on GitHub.