groverburger/grobpaint: Somewhere between MS Paint and Paint.NET. Multiplatform by default. · GitHub

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
• Selection – rectangular and magic wand with live tolerance preview, move/resize/rotate content with handles, 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, editable input + slider), pan (space+drag, middle-click, trackpad), fit-to-view, grid overlay
• File I/O – PNG, JPEG, BMP, GIF; native .gbp project 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 – draggable tabs, multiple images open at once
• Clipboard – copy/paste within app and to/from system clipboard
• Auto-save – all work is persisted to localStorage automatically

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 --browser

Dependencies:

• 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.

.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:

No frameworks, no dependencies beyond one CDN include (JSZip for browser-side .gbp support).

GrobPaint was built with significant help from Claude by Anthropic.