A native GTK4/libadwaita diagram viewer and editor supporting PlantUML and Mermaid syntax, with real-time preview and no Java or Node.js required.
- Native rendering — Graphviz-based, no Java, no Node.js, no browser
- Real-time preview — debounced live update as you type
- Syntax highlighting — for both PlantUML and Mermaid
- Multi-tab editing with auto-close of untouched tabs
- Export to SVG, PNG, and PDF — interactive dialog or headless CLI (
--export) - Auto-format detection — from file extension (
.puml,.mmd) and content keywords - Dark mode — follows system theme, per-diagram dark toggle, 7 color presets with per-slot overrides
- Click-to-source — click a rendered element to jump to its source line
- Outline panel — navigable list of diagram elements with click-to-source
- Zoom & pan — mousewheel zoom-to-cursor, pinch-to-zoom, drag to pan, minimap for large diagrams
- Template gallery (
Ctrl+T) — built-in templates for all diagram types - Diagram tools — stats, linting, validation, complexity analysis, optimization suggestions, beautifier
- Diagram comparison — semantic diff between diagrams or file versions
- Git integration — blame gutter, diff marks, history viewer, repo graph
- Performance monitor — render time display in status bar
- VS Code extension — full-featured extension with live preview, syntax highlighting, snippets, completions, hover info, and outline symbols via built-in LSP server
 |
 |
 |
 |
| Type | Notes |
|---|---|
| Sequence | Participants, messages, notes, groups, lifelines, autonumber |
| Class | Members, relations, visibility, generics, packages, stereotypes |
| Activity | Branches, loops, swimlanes, concurrency, notes, detach |
| State | Composite states, history, fork/join, concurrency, stereotypes |
| Use Case | Actors, system boundaries, extends/includes |
| Component | Interfaces, ports, containers, nesting |
| Object | Instances, maps, links |
| Deployment | Nodes, artifacts, clouds, nesting |
| ER | Entities, relationships, crow's foot notation |
| MindMap | Hierarchical tree, arithmetic notation |
| WBS | Work breakdown structure |
| Gantt | Tasks, sections, milestones, dependencies, critical path |
| JSON | Data tree visualization with syntax highlighting |
| YAML | Data tree visualization with indentation-based nesting |
| Chronology | Vertical timeline of events with dates |
| Timing | Signal state timelines (concise, robust, binary, clock, analog) |
| Network (nwdiag) | Network segments, nodes, addresses, groups |
| Archimate | Business, Application, Technology, Motivation, Physical layers |
| C4 | Context, Container, Component diagrams via stereotypes. Both native and full C4-PlantUML macro syntax. |
| DOT passthrough | Raw Graphviz DOT — @startdot / @enddot |
| Salt (wireframes) | UI mockups with buttons, text fields, checkboxes, dropdowns |
| Chen ER | Chen notation with entities (boxes), relationships (diamonds), attributes (ovals) |
| EBNF | Grammar railroad diagrams from EBNF rules |
| Regex | Regular expression NFA/railroad visualization |
| Tree | Indentation-based tree diagrams |
| Ditaa | ASCII art rendered as monospace diagram |
| Board | Kanban-style board with columns and cards |
gDiagram includes a near-complete PlantUML preprocessor implementation:
!include "local.puml"— local file inclusion with circular-include detection!define NAME VALUEand!define BOX(args) body— simple and parameterized macros!procedure/!unquoted procedure/!function/!return/!endprocedure— multi-line macros and functions!ifdef/!ifndef/!if EXPR/!elseif/!else/!endif— conditional compilation!$var = exprand!$var ?= expr— variable assignment- Default parameter values:
!unquoted procedure Foo($a, $b="default") - Expression evaluator: arithmetic, comparisons,
&&/||/!, string concatenation, function calls - 19 built-in functions:
%substr,%strpos,%strlen,%upper,%lower,%function_exists,%is_dark,%intval,%set_variable_value,%get_variable_value, and more
This is enough to expand the full C4-PlantUML standard library at parse time.
| Type | Notes |
|---|---|
| Flowchart | 11 shapes, 6 arrow types, subgraphs, classDef styling, click handlers |
| Sequence | Actors, messages, notes, loops, autonumber, parallel blocks, activation bars |
| State | States, transitions, start/end, nested states, fork/join concurrency |
| Class | Classes, members, relationships, visibility, generics, annotations |
| ER | Entities, attributes, relationships, cardinality, PK/FK/UK keys |
| Gantt | Tasks, sections, milestones, critical path, dependencies |
| Pie | Data slices, percentages, showData option |
| Git Graph | Branches, commits, merges, tags, commit types |
| User Journey | Tasks, satisfaction scores, sections, multiple actors |
| Mindmap | Hierarchical tree, multiple node shapes, depth-colored nodes |
| Timeline | Chronological events with sections |
| Quadrant | 2×2 quadrant chart with labeled points |
| XYChart | Bar and line charts with axes |
| Kanban | Kanban board with columns and cards |
| Sankey | Flow/energy diagrams with proportional links |
| Requirement | Requirement elements with relationships |
| Block | Grid-layout blocks, groups, directional arrows |
| Packet | Network packet structure, bit-range fields, 32-bit row layout |
| C4 | Context, Container, Component, Dynamic, Deployment diagrams |
| Architecture | Infrastructure topology with services, groups, junctions |
| ZenUML | Code-style sequence diagrams with nested calls |
| Radar | Spider/polar charts for multi-dimensional comparison |
| Treemap | Hierarchical tree with value-proportional leaf sizing |
- Blame gutter — inline
git blameper line, click for full commit detail - Diff marks — line gutter marks for added/changed/removed lines vs HEAD
- History viewer (
Ctrl+Shift+H) — commit log for the current file, side-by-side compare, restore to editor, open in Meld - Repo graph (
Ctrl+Shift+G) — live Mermaid gitGraph of the repository with branch filtering and commit detail panel
Download the latest release from the Releases page.
# Debian/Ubuntu
sudo dpkg -i gdiagram_*.debDebian/Ubuntu:
sudo apt install meson ninja-build valac \
libgtk-4-dev libadwaita-1-dev libgtksourceview-5-dev \
libgee-0.8-dev libgraphviz-dev librsvg2-dev libcairo2-dev \
libsoup-3.0-dev libjson-glib-dev \
gettext graphvizFedora:
sudo dnf install meson ninja-build vala \
gtk4-devel libadwaita-devel gtksourceview5-devel \
libgee-devel graphviz-devel librsvg2-devel cairo-devel \
libsoup3-devel json-glib-devel gettext graphvizArch Linux:
sudo pacman -S meson ninja vala gtk4 libadwaita gtksourceview5 \
libgee graphviz librsvg cairo libsoup3 json-glib gettextNote: gDiagram requires a patched Graphviz build for correct HTML table cell text centering in activity diagrams. See
patches/andscripts/build-patched-graphviz.sh.
meson setup build --prefix=/usr
meson compile -C build
sudo meson install -C build./build/src/gdiagramgdiagram # open empty editor
gdiagram diagram.puml # open a PlantUML file
gdiagram diagram.mmd # open a Mermaid file
# Headless export (no GUI required)
gdiagram -e output.png diagram.puml # export to PNG
gdiagram -e output.svg -f svg diagram.mmd # export to SVG
gdiagram -e output.pdf -f pdf diagram.puml # export to PDFSee docs/KEYBOARD_SHORTCUTS.md for the full list. Key shortcuts:
| Shortcut | Action |
|---|---|
Ctrl+S |
Save |
Ctrl+E |
Export (PNG/SVG/PDF) |
Ctrl+T |
Template gallery |
Ctrl+Shift+H |
Git history for current file |
Ctrl+Shift+G |
Git repository graph |
Ctrl+? |
Keyboard shortcuts overlay |
gDiagram includes a VS Code extension powered by the gdiagram-lsp language server.
# Install the LSP server (included in the .deb package)
sudo dpkg -i gdiagram_*.deb
# Build and install the VS Code extension
cd vscode-extension
npm install && npx @vscode/vsce package
code --install-extension gdiagram-0.1.0.vsix- Live preview (
Ctrl+Shift+V) — side-by-side SVG rendering with zoom, pan, and click-to-source - Syntax highlighting — TextMate grammars for PlantUML and Mermaid
- Snippets — 49 snippets covering all 50 diagram types (
puml-*andmmd-*prefixes) - Completions — keyword completions per diagram type
- Hover — documentation on hover for keywords
- Outline — document symbols in the outline panel
- Export — PNG/SVG/PDF via command palette
- Template gallery — "New Diagram from Template" with all 50 types
- Diagnostics — parse errors as VS Code Problems
The examples/ directory contains ready-to-open diagram files covering all supported types.
See docs/QUICK_START.md for a guided introduction.
Architecture diagrams (rendered by gDiagram itself) are in docs/architecture/:
- Architecture Overview — layers, components, dependencies
- Rendering Pipeline — source → parse → render → display flow
- Class Hierarchy — key class relationships
- Diagram Types — parser/AST/renderer triples for all 42 types
- UI Interaction Flows — user action sequences
dpkg-buildpackage -us -uc -bflatpak-builder --user --install build-flatpak org.gnome.gDiagram.jsoncd appimage && appimage-builder --recipe AppImageBuilder.ymlGNU General Public License v3.0 — see LICENSE.
- PlantUML for the diagram syntax
- Graphviz for diagram rendering
- GTK and libadwaita for the UI framework