kUML

kUML is a developer-oriented modeling tool that expresses diagrams and related models as Kotlin code. It suits teams that want modeling in their development workflow, especially when they need several notations or generated artifacts. Its reach is broad for a free Apache 2.0 project, though the code-based approach requires care with trusted workspaces.

Overview

kUML brings UML 2.x, SysML 2, C4, BPMN 2.0 and ERM into a type-safe Kotlin DSL. Support for all 14 UML 2.x diagram types gives software teams room to describe structure, behavior and deployment in one tool. The trade-off is that modeling happens through Kotlin rather than a conventional drawing-first workflow, making it a stronger fit for developers than for occasional diagram authors.

Workflows span the CLI, Gradle, IntelliJ, VS Code, Obsidian and Asciidoctor, with a Compose Multiplatform desktop app distributed as a macOS cask. Structurizr DSL round-trip and optional XMI interoperability help teams exchange models. The online handbook covers installation and usage.

Key features

Modeling and validation

Compile-time validation and IDE support bring familiar feedback into model authoring. That can help teams maintain models alongside source code, where errors can be caught as part of the coding process. Reverse engineering is supported, further suiting software-centered workflows.

AI and code generation

An MCP server supports agent introspection, and the kuml ai subcommand enables AI-assisted modeling. Built-in transformations generate JPA, OpenAPI 3.0 YAML, Kubernetes manifests and Dockerfiles. These outputs make kUML more than a diagram repository for teams that can use generated artifacts in their engineering process; readers seeking only visual documentation may not benefit from that breadth.

Interoperability and execution safety

Structurizr DSL round-trip and optional XMI support provide routes to work across modeling formats. The MCP authoring server validates scripts with KumlScriptGuard before evaluation and uses the same sandboxing as the CLI render and validate commands. Even so, rendering Kotlin scripts executes their source code. The handbook advises using only scripts or workspaces you trust, a real operational consideration when accepting model files from others.

Pricing

kUML is free and open source under Apache 2.0. The Free / open source plan costs nothing and has no stated feature limits. That makes it straightforward for individual developers and teams to adopt without a subscription; there are no paid tiers to weigh.

Platforms

kUML supports Windows, macOS, Linux and web browsers, with both self-hosted and API options. Distribution includes Homebrew for macOS and Linux, Chocolatey and MSI for Windows, native DEB, RPM and DMG packages, Docker, and library modules on Maven Central. The desktop app is distributed as a macOS cask, so the wider platform support comes through the other installation and integration options.

Who it's for

kUML is best for developers and engineering teams comfortable expressing models in Kotlin, particularly those working across multiple modeling notations or wanting diagrams connected to generated implementation artifacts. Its CLI, Gradle and IDE integrations make it a natural candidate for code-centric workflows. It is less suited to users who want to create diagrams without working in source code or evaluating scripts.

Pros and cons

• Broad modeling coverage: UML 2.x, SysML 2, C4, BPMN 2.0 and ERM cover varied software and systems modeling needs.
• Useful development feedback: Compile-time validation and IDE support suit models maintained as part of software work.
• Practical generated outputs: JPA, OpenAPI, Kubernetes and Docker artifacts can connect modeling to implementation.
• Open source with broad integrations: Apache 2.0 licensing and integrations across command-line, build, IDE and documentation workflows give teams flexibility.
• Code execution demands trust: Rendering Kotlin scripts runs source code, so shared or external workspaces require care.
• Developer-centered authoring: The Kotlin DSL is a barrier for users looking for a drawing-first diagramming tool.

Alternatives

For a wider selection of UML tools, browse UML Modeling Software. Consider Sparx Enterprise Architect if its freemium model and free trial better suit your evaluation needs. BESSER is another free, open-source option with no freemium tier or hidden fees. UMLet may fit readers who want a free UML tool available as a standalone desktop app, Eclipse plugin, web app or VS Code extension. ArgoUML is a free, open-source option for Windows, macOS and Linux. BOUML is another free option for those desktop platforms. BridgePoint includes an editor, verifier and model compilers in its free Apache 2.0 open-source edition. Eclipse Papyrus offers a free open-source modeling environment with no usage limits stated. Gaphor is a free, open-source alternative under Apache 2.

Verdict

Choose kUML if you want a free, extensible way to maintain multiple kinds of models in Kotlin and connect them to validation, integrations and code generation. The breadth and development workflow are its strongest reasons to adopt it. Look elsewhere if you need a drawing-first experience or cannot ensure that the Kotlin scripts in your modeling workspace are trusted.