PlantUML Diagram Editor

Edit PlantUML class and sequence diagrams visually — right inside VS Code.

This extension gives you a split-view workflow: write PlantUML notation in the text editor on one side, and see a live, interactive diagram on the other. Changes flow both ways, edit the text, save, and the diagram updates, edit the diagram, save, and the text updates.

Built on the Graphical Language Server Platform (GLSP).

Features

Visual diagram editing — Select, move, rename, and delete elements directly on the rendered diagram. Double-click any label to edit it inline (use Shift+Enter for multi-line editing where supported).

Bidirectional synchronization — The .puml source file and the diagram stay in sync. Save the file to push text changes into the diagram; edits made on the diagram are written back to the source.

Real-time diagnostics — An integrated LSP server highlights syntax errors as you type and offers code completions for PlantUML keywords, arrow types, and existing entity names.

SVG export — Export your diagram to .svg from the tool palette.

Plugin architecture — Drop JAR files into the plugins/ directory to add custom validation rules or entirely new diagram modules.

Supported diagram types

• Class diagrams — entities, attributes, methods, relationships, labels, layout, notes
• Sequence diagrams — participants, messages, labels, groups, notes

Requirements

The extension bundles everything else it needs. Java is required because the GLSP server and PlantUML parser run on the JVM.

Getting started

1. Install the extension from the Marketplace.
2. Open any .puml file.
3. Click "Open PlantUML Preview" in the editor toolbar.
4. The diagram panel opens to the right — start editing.

Usage tips

• Rename elements — double-click a label on the diagram and type a new name.
• Delete elements — select an element and use the delete tool in the tool palette.
• Multi-line labels — press Shift+Enter while editing a label to insert a line break.

Extending with plugins

Custom validation rules

Implement the ValidationRule interface, package as a JAR, and place it in the plugins/ directory. The rule will be picked up on the next server startup.

Custom diagram modules

Extend DiagramModule from GLSP, and drop the JAR into your <user>/.glsp-plantuml/plugins directory.

Known limitations

• Only class and sequence diagrams are supported out of the box.
• The diagram preview requires Java 21+ to be available on PATH or configured via java.home.
• For changing between two diagram types, the editor must be closed and just the source code open.
• PlantUML skinparam and CSS styling is not supported.

License

GPL-2.0-only WITH Classpath-exception-2.0