What is UMLet?

UMLet is a free, open-source UML tool built for fast UML sketching. Its defining idea is that you modify UML elements through text input and a small markdown-like dialect instead of pop-up dialogs. It runs as a stand-alone app on Windows, macOS, and Linux, as an Eclipse plugin, as a web app called UMLetino, and as a Visual Studio Code extension. If you want to draw UML diagrams quickly without fighting dialog boxes, UMLet is aimed at you; if you need a full model-driven tool with a repository and code generation, it is not that.

What UMLet is for

UMLet targets quick, lightweight UML sketches rather than heavyweight modeling. The current release shown on the site is UMLet 15.1, described as a "Free UML Tool for Fast UML Diagrams."

Supported diagram types include:

• Class diagrams
• Use case diagrams
• Sequence diagrams
• State diagrams
• Deployment diagrams
• Activity diagrams

Sequence and activity diagrams can be created from plain text, which fits the tool's text-first approach.

How the text-based editing works

Instead of opening a properties dialog for each element, you select an element and edit it in the lower-right text panel using a small markdown dialect. This is the core concept the project describes in a paper.

The practical consequences:

• Speed: you type changes rather than click through dialogs.
• Templates: elements can be modified inside their palettes and immediately reused as new templates, so you can tailor UMLet to your modeling needs.
• Custom elements: you can create your own UML elements. An element's look can be changed at run-time by editing a few lines of Java code, which UMLet compiles on the fly, so new element types can be added without leaving the tool.

Quickstart

The site's own quickstart lists these operations:

1. Add elements to a diagram with a double click.
2. Edit elements using the lower-right text panel.
3. Use Ctrl+Space for context-sensitive help.
4. Select multiple elements using Ctrl or a lasso.
5. Press C to copy the diagram to the system clipboard.
6. Use +/- or Ctrl+mousewheel to zoom.
7. Press Shift to avoid sticking relations.

The expected result is a diagram you can assemble and adjust entirely from the canvas plus the text panel, without modal dialogs.

Sharing and export

Diagrams can be exported to EPS, PDF, JPG, SVG, and the clipboard. Version 15.0 added hi-res export, along with web zoom, lasso, export, dark mode, and startup changes. Version 15.1 included a relation bug fix, a log library update, and dark mode cleanup.

Where you can run it

Cost and licensing

UMLet is described as free and open-source. The site links to its GitHub repository and offers sponsorship via GitHub, Patreon, or PayPal. Sponsorship is optional support for the project, not a purchase requirement.

When to choose something else

UMLet fits fast sketching and text-driven editing. If your work depends on a shared model repository, round-trip code generation, or team-wide model governance, those needs point to a different class of tool. For quick diagrams, custom elements, and script-like editing, UMLet's combination of a simple UI and text input is the reason to pick it.