License guide
Open-source UML tools.
Compare editors and diagram generators without treating every “free” offer as the same licensing model.
Checked Oct 22, 2026Technical University of Munich
Apollon
An open-source web UML editor maintained at TUM, offering thirteen diagram types and real-time collaboration.
Checked Oct 22, 2026clang-uml project
clang-uml
An open-source reverse-engineering tool that generates class, sequence, package, and other diagrams from C and C++ code in PlantUML, Mermaid, or JSON form.
Checked Oct 22, 2026crystal-facet-uml project
crystal-facet-uml
An open-source Windows UML tool that keeps model elements, names, hierarchy, and relationships consistent across multiple diagrams.
Checked Oct 22, 2026JGraph
diagrams.net Desktop
The open-source Electron desktop edition of diagrams.net, a cross-platform drawing application with UML shape libraries and a matching browser edition.
Checked Oct 22, 2026Gaphor project
Gaphor
An open-source graphical modeling environment implemented in Python with support for UML and part of SysML v1.
Checked Oct 22, 2026JetUML project
JetUML
A lightweight open-source UML diagram editor derived from Violet UML and using JSON as its model storage format.
Checked Oct 22, 2026kUML project
kUML
A model-oriented textual DSL built with Kotlin, covering UML, SysML v2, C4, and BPMN with desktop, web, command-line, and IDE integrations.
Checked Oct 22, 2026LSP UML project
LSP UML
An open-source VS Code extension that derives UML class, sequence, activity, and use-case diagrams from a running language server.
Checked Oct 22, 2026Modeliosoft
Modelio
An open-source UML and BPMN modeling environment with collaboration-oriented features and support for shared model storage.
Checked Oct 22, 2026Eclipse Foundation
Papyrus Web
A browser-based evolution of Eclipse Papyrus for UML 2.5 modeling, extensible diagrams, and model-driven engineering workflows.
Checked Oct 22, 2026PlantUML project
PlantUML
An open-source text-to-diagram generator that produces UML-style diagrams and integrates with many editors, documentation systems, and build workflows.
Checked Oct 22, 2026py2puml project
py2puml
An open-source reverse-engineering utility that creates PlantUML class diagrams from Python applications.
Checked Oct 22, 2026State Machine cat project
State Machine cat
A text-based state-machine diagram generator with a compact DSL and support for compound states, entry and exit actions, transitions, and SCXML import and export.
Checked Oct 22, 2026StateSmith project
StateSmith
An open-source state-machine code generator supporting multiple programming languages and several diagram-authoring workflows.
Checked Oct 22, 2026KDE
Umbrello
An open-source UML modeling application from the KDE ecosystem, primarily distributed for Linux.
Checked Oct 22, 2026Umple project
Umple
An open-source model-oriented programming environment that combines textual and graphical modeling and generates Java, PHP, and Ruby code.
Checked Oct 22, 2026Violet UML project
Violet UML Editor
A long-running lightweight UML diagram editor that resumed active updates in 2026.
Open source is only one selection dimension
The application license, hosted service, plugin ecosystem, and enterprise extensions may use different commercial models. NeoMBSE records these separately wherever the evidence allows.