Aliot UML Editor

Edit UML visually. Keep your PlantUML source.

Create and edit diagrams directly in VS Code: rename a class, connect components, rearrange a workflow, or change the source. Aliot UML Editor keeps the canvas and supported PlantUML syntax in sync, with editable shapes instead of a rendered image.

33 diagram families · Visual and source editing · Plain PlantUML files · Runs locally · MIT licensed

The actual editor, shown in its standalone preview with the bundled Order model example.

Why Aliot UML Editor?

• Work directly on the diagram. Double-click names and members, add elements from the canvas menu, and drag between connection handles for supported relationships.
• Keep readable source. Edit .puml files or use the source panel inside the canvas. Source edits update the diagram; visual edits update the corresponding source.
• Start from a template. Choose from 33 diagram families in a searchable gallery, then switch between multiple diagram blocks in the same file.
• Your PlantUML stays plain PlantUML. Manual positions go to a small layout file next to the diagram, so other tools and teammates without the extension see exactly the source you wrote.
• Use familiar editor controls. One undo/redo history for moves and edits, native VS Code save and unsaved-change handling, plus outline navigation, a minimap, zoom, fit, and Re-layout.
• Render locally. No Java, Graphviz installation, PlantUML server, or remote rendering service is required.

Get started

Requires VS Code 1.104.0 or later on a desktop or remote extension host.

1. Install Aliot UML Editor from the Extensions view, or run ext install voidaliot.aliot-uml-editor from Quick Open (Ctrl+P / Cmd+P). For a downloaded .vsix, use Extensions: Install from VSIX… from the Command Palette.
2. Run Aliot UML: New Diagram and choose a template, or open an existing .puml, .plantuml, .pu, or .iuml file.
3. Double-click a label or compartment to edit it. Right-click empty canvas to add an element. Drag connection handles to create supported relationships.
4. Save with Ctrl+S / Cmd+S. Manual positions are saved automatically in the layout file.

If a file opens as text, right-click its editor tab and choose Reopen Editor With… → Aliot UML Editor, or run Aliot UML: Open Diagram.

Pick a starter and make it your own. The gallery includes 33 native diagram types.

From architecture to workflows

Model a checkout conversation, sketch a service boundary, explore a data structure, or map a release plan. Each family has its own native notation and editing tools.

Sequence diagrams keep participants, messages, and lifelines on the canvas.

Activity diagrams arrange actions, decisions, and merges around the control flow.

Visual editing and source, together

Open Edit PlantUML source in canvas from the toolbar to work on the current diagram's text. Apply a source draft with Apply or Ctrl+Enter / Cmd+Enter. For plain PlantUML files, Source file opens the text document alongside the diagram.

Try this in a new order.puml file:

@startuml
class Order {
  +number: String
  +submit()
}
class "Line item" as LineItem {
  +quantity: Integer
}
Order "1" *-- "many" LineItem : contains
@enduml

Double-click Order to rename it, edit its members, or move the shapes. Use Re-layout to clear manual placements and arrange the current diagram again.

Where your layout is saved

Commit the layout file to share your arrangement, or ignore it and let everyone use the automatic layout. Renaming, moving or deleting a diagram in VS Code does the same to its layout file; outside VS Code, move both together. Pan and zoom stay in your workspace and are not shared. See the layout file format.

Canvas shortcuts

Connections in structured activities, trees, and networks follow their source structure. Gantt tasks and chronology events change their dates when dragged.

Sequence lifelines offer connection points at the message rows. Drag between lifelines at the desired row to insert a message there. Moving messages or dividers between rows updates their source order; divider widths and horizontal placement are saved with the layout.

PlantUML compatibility

Preview release. Aliot UML Editor implements a native subset of PlantUML; support for a diagram family does not mean complete language compatibility or identical rendering to PlantUML. Unsupported constructs retain their source and produce diagnostics.

Common labels, relationships, nested groups, and selected styles are supported. Full styling, arbitrary preprocessing, custom sprites, and external includes are not evaluated. Known C4 and ArchiMate macros are interpreted locally. Diagram layout and appearance use the native editor.

Desktop and remote VS Code hosts are supported. A browser extension bundle for vscode.dev is not currently provided. Image and PDF export are not currently offered.

See the native editing reference for the scope of each family and the layout file format for saved positions. The bundled examples include all 33 starter diagrams.

Feedback and contributing

Found a diagram that does not round-trip, or a construct you would like supported? Open an issue with a minimal .puml sample. See Contributing for the architecture, development setup, and test commands, and the Changelog for release notes.

License

MIT — free to use, modify, and distribute, including commercially, under the license terms. Copyright © 2026 Aliot UML Editor contributors.

Bundled dependencies retain their own licenses. See Third-party notices and Third-party license texts.