Somewhere between MS Paint and Paint.NET. Multiplatform by default.
Paint.NET doesn't run on macOS. GrobPaint fills that gap: a lightweight image editor with layers, blend modes, and selection tools, built with web technologies and a tiny Python backend. The goal isn't to clone Paint.NET or compete with Photoshop. It's to have the tools you actually need without the bloat.
- Layers - add, delete, duplicate, merge, reorder, per-layer opacity and blend modes (16 modes)
- Tools - Pencil, Brush, Eraser, Fill, Eyedropper, Line, Rectangle, Ellipse, Text, Select, Magic Wand, Move, Rotate, Scale, Mirror
- Selection - rectangular and magic wand with configurable tolerance, copy/cut/paste, crop to selection
- Color - HSV picker, RGB/Hex input, alpha channel, palettes (Lospec 500, PICO-8), swap primary/secondary
- Canvas - zoom (scroll wheel, pinch, keyboard), pan (space+drag, middle-click, trackpad), fit-to-view, grid overlay
- File I/O - PNG, JPEG, BMP, GIF; native
.gbpproject format preserves layers as a ZIP archive - Sprite sheets - split a sheet into layers, or export layers as a horizontal sheet
- Image operations - scale (nearest/bilinear/bicubic), canvas resize with anchor, flip, flatten
- Multi-document - tabbed interface, multiple images open at once
- Clipboard - paste images directly from clipboard as new layers
This launches a native window using pywebview. If pywebview isn't installed, it falls back to your default browser.
To force browser mode:
python grobpaint.py --browserDependencies:
- Python 3.9+
pywebview(optional, for native window) -pip install pywebview
No npm, no bundler, no build step. The frontend is vanilla JS with ES modules.
Produces dist/GrobPaint.app (macOS) or dist/GrobPaint/GrobPaint (binary) via PyInstaller.
You can also open index.html directly or serve it with any static file server. File dialogs won't be available, but the editor falls back to browser file input and download for open/save.
| Shortcut | Action |
|---|---|
P B E F I L R O T S W M |
Tool hotkeys |
[ / ] |
Decrease / increase brush size |
X |
Swap primary/secondary colors |
+ / - |
Zoom in / out |
Ctrl+0 |
Fit in view |
Ctrl+1 |
Actual size (100%) |
Ctrl+N |
New image |
Ctrl+O |
Open file |
Ctrl+S |
Save |
Ctrl+Shift+S |
Save as |
Ctrl+Z / Ctrl+Shift+Z |
Undo / redo |
Ctrl+C / Ctrl+X / Ctrl+V |
Copy / cut / paste |
Ctrl+A / Ctrl+D |
Select all / deselect |
Ctrl+G |
Toggle grid |
Delete |
Delete selection |
Space + drag |
Pan canvas |
.gbp files are ZIP archives containing:
manifest.json # dimensions, layer metadata (name, opacity, visibility, blend mode)
layers/
layer_0.png
layer_1.png
...
The app is ~2500 lines of vanilla JavaScript split across four modules:
| File | Role |
|---|---|
js/core.js |
EventBus, Layer, History (swap-based undo/redo), PaintDocument, Selection |
js/renderer.js |
Compositing engine, checkerboard background, zoom/pan, grid overlay |
js/tools.js |
All tools, flood fill, flood select, Bresenham line |
js/ui.js |
Color system, HSV picker, layers panel, document tabs, menus, dialogs |
js/app.js |
App init, canvas events, keyboard shortcuts, file I/O |
grobpaint.py |
Python HTTP server + pywebview launcher, native file dialogs |
No frameworks, no dependencies beyond one CDN include (JSZip for browser-side .gbp support).
GrobPaint was built with significant help from Claude by Anthropic.