Top 10 Open-Source Alternatives to PlantUML in 2025

As diagramming and modeling tools evolve, the search for robust open-source alternatives to PlantUML continues. Here's a comprehensive look at the top 10 tools to consider in 2025.

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1. Mermaid

Description: Mermaid is a JavaScript-based diagramming tool using a Markdown-inspired syntax to create diagrams. It integrates seamlessly into web environments.
Key Features:
Supports various diagrams like sequence, flowcharts, and Gantt charts.
Directly renderable in Markdown files on GitHub.
Customizable styling with CSS.
Embeddable into JavaScript pages.
Active open-source community support.
License: MIT license
Website: Visit Mermaid
Source: GitHub Repository

2. D2

Description: D2 is a modern diagram scripting language that simplifies creating complex diagrams with an expressive syntax.
Key Features:
Text-based syntax for defining diagrams.
Supports various diagram types.
Integration with multiple layout engines.
Provides an online playground for testing.
100% FOSS.
License: Open-source
Website: Discover D2
Source: GitHub Repository

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3. UMLet

Description: UMLet is a lightweight UML tool with a focus on speed and user-friendly interface for rapid diagram creation.
Key Features:
Drag-and-drop for quick UML diagram creation.
Text-based input for sequence and activity diagrams.
Exports to formats like EPS, PDF, JPG, SVG.
Available as a standalone application or an Eclipse plugin.
Customizable UML elements.
License: Open-source
Website: Explore UMLet
Source: GitHub Repository

4. ArgoUML

Description: ArgoUML is a Java-based UML modeling tool designed to handle large models with object-oriented support.
Key Features:
Supports all standard UML diagram types.
Code generation and reverse engineering capabilities.
Project management features for team collaboration.
"Critic" feature for requirements management.
License: Open-source
Website: Visit ArgoUML
Source: SourceForge Repository

5. Gaphor

Description: Gaphor is a desktop application for modeling and diagramming, supporting popular standards in software architecture.
Key Features:
Supports UML, SysML, RAAML, and C4 model standards.
Cross-platform: Windows, macOS, and Linux.
Create class, interaction, and state machine diagrams.
Customizable extensions and plugins.
License: Apache 2.0 license
Website: Learn More About Gaphor
Source: GitHub Repository

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6. Structurizr

Description: Structurizr allows creating multiple diagrams from a single model using a DSL, designed for the C4 model of software architecture.
Key Features:
Diagrams as code with Structurizr DSL.
Version control for architecture diagrams.
Support for the C4 model.
Integrated documentation tools.
License: Apache License 2.0
Website: Discover Structurizr
Source: GitHub Repository

7. Umbrello

Description: Umbrello is a free, cross-platform UML diagram tool that creates standard UML diagrams.
Key Features:
Creates standard UML diagrams.
Imports diagrams from code in multiple languages.
Generates code from diagrams.
XML Metadata Interchange (XMI) for diagrams.
License: Open-source
Website: Visit Umbrello
Source: KDE Repository

8. Draw.io (diagrams.net)

Description: Draw.io, now known as diagrams.net, provides free, robust diagramming both online and offline, with a wide range of diagram types.
Key Features:
Real-time collaboration.
Offline desktop application for security-sensitive environments.
Various storage options like local, Google Drive, and OneDrive.
Supports UML, C4, ArchiMate, BPMN, and SysML shapes.
Icon packs for AWS, Azure, GCP, Cisco, and Kubernetes.
License: Open-source
Website: Explore Draw.io
Source: GitHub Repository

9. Archi

Description: Archi is an open-source modeling tool for creating ArchiMate models, aimed at users needing ArchiMate without heavy financial investment.
Key Features:
Supports ArchiMate 3.1 language.
Creates ArchiMate elements, relationships, and views.
Includes hints for understanding the ArchiMate language.
Visualizer for showing relationships.
License: Open-source
Website: Visit Archi
Source: GitHub Repository

10. Kroki

Description: Kroki supports creating diagrams from various textual description languages, designed for versatility and ease of use.
Key Features:
Supports many diagram languages.
Simple integration into web applications or CI/CD pipelines.
Create diagrams from text with ease.
Open-source and free to use.
License: Open-source
Website: Discover Kroki
Source: GitHub Repository

These tools offer a diversity of approaches to diagramming, from text-based languages to visual interfaces. Your specific needs and preferences will determine the most suitable choice for your projects in 2025.

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FAQ

1. What is Mermaid and what are its key features?

Mermaid is a JavaScript-based diagramming tool that uses a Markdown-inspired syntax to create diagrams. It can render various diagrams like sequence diagrams, flowcharts, and Gantt charts, and can be directly embedded in web pages and Markdown files. Learn more about Mermaid | Explore Mermaid on GitHub

2. What is D2 and how does it facilitate diagram creation?

D2 is a modern diagram scripting language that simplifies the creation of complex diagrams with a text-based syntax. It supports multiple diagram types and integrates with various layout engines. Discover D2 | Check out D2 on GitHub

3. How does UMLet enhance UML diagram creation?

UMLet is a lightweight, open-source UML tool that allows rapid diagram creation with a simple user interface and supports exporting to various formats. It is available as both a standalone application and an Eclipse plugin. Learn more about UMLet | Explore UMLet on GitHub

4. What are ArgoUML's capabilities in UML modeling?

ArgoUML is a Java-based UML modeling tool that supports all standard UML diagram types, includes code generation, reverse engineering capabilities, and features for project management and team collaboration. Discover ArgoUML | Explore ArgoUML on SourceForge

5. What standards does Gaphor support and where can it be used?

Gaphor supports UML, SysML, RAAML, and C4 model standards and is available for Windows, macOS, and Linux. It allows building of class, interaction, and state machine diagrams and can be extended with custom plugins. Learn more about Gaphor | Explore Gaphor on GitHub

6. How does Structurizr utilize diagrams as code?

Structurizr allows creation of multiple diagrams from a single model using a DSL. It supports version control for architecture diagrams and includes tools for documentation, particularly supporting the C4 model for software architecture. Discover Structurizr | Check out Structurizr on GitHub

7. What features does Umbrello offer for UML diagram creation?

Umbrello is an open-source UML diagram tool available for Linux, Windows, and macOS that can create standard UML diagrams, import diagrams from code, and generate code from diagrams. Learn more about Umbrello | Explore Umbrello on KDE

8. What makes Draw.io (diagrams.net) a versatile diagramming tool?

Draw.io (diagrams.net) is a free, open-source tool that offers real-time collaboration capabilities, offline desktop application, and support for various storage options. It supports UML, C4, ArchiMate, BPMN, and SysML shapes. Discover Draw.io | Explore Draw.io on GitHub

9. How does Archi benefit users working with the ArchiMate language?

Archi is an open-source tool for creating ArchiMate models and sketches, supporting the latest ArchiMate 3.1 language. It includes hints for understanding the ArchiMate language and tools for creating complex elements and relationships. Learn more about Archi | Explore Archi on GitHub

10. What is Kroki and how does it support diagram creation?

Kroki is a tool that supports creating diagrams from a variety of textual description languages. It is versatile, easy to use, and can be integrated into web applications or CI/CD pipelines. Discover Kroki | Explore Kroki on GitHub

References

About the Author

Violetta Bonenkamp, also known as MeanCEO, is an experienced startup founder with an impressive educational background including an MBA and four other higher education degrees. She has over 20 years of work experience across multiple countries, including 5 years as a solopreneur and serial entrepreneur. She’s been living, studying and working in many countries around the globe and her extensive multicultural experience has influenced her immensely.

Violetta is a true multiple specialist who has built expertise in Linguistics, Education, Business Management, Blockchain, Entrepreneurship, Intellectual Property, Game Design, AI, SEO, Digital Marketing, cyber security and zero code automations. Her extensive educational journey includes a Master of Arts in Linguistics and Education, an Advanced Master in Linguistics from Belgium (2006-2007), an MBA from Blekinge Institute of Technology in Sweden (2006-2008), and an Erasmus Mundus joint program European Master of Higher Education from universities in Norway, Finland, and Portugal (2009).

She is the founder of Fe/male Switch, a startup game that encourages women to enter STEM fields, and also leads CADChain, and multiple other projects like the Directory of 1,000 Startup Cities with a proprietary MeanCEO Index that ranks cities for female entrepreneurs. Violetta created the "gamepreneurship" methodology, which forms the scientific basis of her startup game. She also builds a lot of SEO tools for startups. Her achievements include being named one of the top 100 women in Europe by EU Startups in 2022 and being nominated for Impact Person of the year at the Dutch Blockchain Week. She is an author with Sifted and a speaker at different Universities. Recently she published a book on Startup Idea Validation the right way: from zero to first customers and beyond and launched a Directory of 1,500+ websites for startups to list themselves in order to gain traction and build backlinks.

For the past several years Violetta has been living between the Netherlands and Malta, while also regularly traveling to different destinations around the globe, usually due to her entrepreneurial activities. This has led her to start writing about different locations and amenities from the POV of an entrepreneur. Here’s her recent article about the best hotels in Italy to work from.

About the Publication

Fe/male Switch is an innovative startup platform designed to empower women entrepreneurs through an immersive, game-like experience. Founded in 2020 during the pandemic "without any funding and without any code," this non-profit initiative has evolved into a comprehensive educational tool for aspiring female entrepreneurs.The platform was co-founded by Violetta Shishkina-Bonenkamp, who serves as CEO and one of the lead authors of the Startup News branch.

Mission and Purpose

Fe/male Switch Foundation was created to address the gender gap in the tech and entrepreneurship space. The platform aims to skill-up future female tech leaders and empower them to create resilient and innovative tech startups through what they call "gamepreneurship". By putting players in a virtual startup village where they must survive and thrive, the startup game allows women to test their entrepreneurial abilities without financial risk.

Key Features

The platform offers a unique blend of news, resources,learning, networking, and practical application within a supportive, female-focused environment:

Skill Lab: Micro-modules covering essential startup skills
Virtual Startup Building: Create or join startups and tackle real-world challenges
AI Co-founder (PlayPal): Guides users through the startup process
SANDBOX: A testing environment for idea validation before launch
Wellness Integration: Virtual activities to balance work and self-care
Marketplace: Buy or sell expert sessions and tutorials

Impact and Growth

Since its inception, Fe/male Switch has shown impressive growth:

3,000+ female entrepreneurs in the community
100+ startup tools built
5,000+ pieces of articles and news written

Partnerships

Fe/male Switch has formed strategic partnerships to enhance its offerings. In January 2022, it teamed up with global website builder Tilda to provide free access to website building tools and mentorship services for Fe/male Switch participants.

Recognition

Fe/male Switch has received media attention for its innovative approach to closing the gender gap in tech entrepreneurship. The platform has been featured in various publications highlighting its unique "play to learn and earn" model.