gns3theme

A Python tool that adds custom color themes to the GNS3 GUI. Works on Linux and macOS.

• 17 built-in color schemes (dark and light variants)
• Custom user schemes via JSON files
• Canvas link color, grid color, label color, and console text color
• Optional device symbol pack
• Auto-detects GNS3 installation (GNS3.app, pip, brew, source)
• Safe patching with automatic backups

Quick start

git clone https://github.com/n3oxmind/gns3theme.git
cd gns3theme

# Apply a theme (auto-detects GNS3 location)
sudo ./gns3theme.py -s nord

# Restart GNS3 and select:
#   Edit -> Preferences -> General -> Interface Style -> Custom

Note: sudo is required when GNS3 is installed system-wide or as a macOS .app bundle. If GNS3 is installed in your home directory (~/.local/), sudo is not needed.

Usage

gns3theme -s <scheme>                     # apply theme (auto-detect GNS3)
gns3theme -s <scheme> --gns3-dir PATH     # apply theme to specific path
gns3theme --restore                       # restore original GNS3 files
gns3theme --ls                            # list available color schemes
gns3theme --symbols                       # install bundled device symbols
gns3theme -s <scheme> --symbols           # apply theme and install symbols

Full options

main arguments:
  -s, --scheme NAME  color scheme to apply and install
  --gns3-dir PATH    GNS3 site-packages path (auto-detected if omitted)

color overrides:
  --bg COLOR         primary background color
  --bg2 COLOR        secondary background color
  --fg COLOR         primary foreground color
  --fg2 COLOR        secondary foreground color
  --tbg COLOR        toolbar background color
  --sbg COLOR        selection background color
  --sfg COLOR        selection foreground color
  --lc COLOR         link color on canvas
  --gc COLOR         grid color
  --lbl COLOR        device label text color

flags:
  --help             show this help
  --ls               list available color schemes
  --symbols          install bundled device symbols to ~/GNS3/symbols/
  --restore [PATH]   restore original GNS3 files from backups

Color schemes

Dark

Scheme	Source
nord	nordtheme
dracula	dracula
tokyonight	enkia
tokyonight-storm	enkia
catppuccin-mocha	catppuccin
one-dark	Atom
monokai	Wimer Hazenberg
gruvbox-dark	morhetz
solarized-dark	Ethan Schoonover
n30x-dark	n30x
n30x-darkblue	n30x

Light

Scheme	Source
tokyonight-light	enkia
catppuccin-latte	catppuccin
gruvbox-light	morhetz
solarized-light	Ethan Schoonover
tomorrow	Chris Kempson

Custom schemes

Create a JSON file in ~/.config/gns3theme/schemes/:

{
  "bg":    "#1e1e2e",
  "bg2":   "#181825",
  "fg":    "#cdd6f4",
  "fg2":   "#b4befe",
  "sbg":   "#585b70",
  "sfg":   "#cdd6f4",
  "tbg":   "#11111b",
  "lc":    "#cdd6f4",
  "gc":    "#232334",
  "color": "dark"
}

Save it as ~/.config/gns3theme/schemes/mytheme.json, then use it with -s mytheme.

Required keys

Key	Description
bg	Primary background
bg2	Secondary background (sidebars, inputs)
fg	Primary foreground / text
fg2	Accent color (section headers)
sbg	Selection background
sfg	Selection foreground
tbg	Toolbar background
color	"dark" or "light"

Optional keys

Key	Description
lc	Link color on canvas (defaults to fg)
gc	Grid color
lbl	Device label text color (defaults to fg)
lw	Link width (float, e.g. 1.2)

Overriding individual colors

You can override any color on top of a base scheme:

# Use nord but with a custom selection background
./gns3theme.py -s nord --sbg 5e81ac

# Use dracula but change the link color
./gns3theme.py -s dracula --lc ff79c6

Device symbols

gns3theme includes 16 SVG device symbols (routers, switches, firewalls, servers, PCs, clouds).

./gns3theme.py --symbols

Symbols are installed to ~/GNS3/symbols/ and appear in the GNS3 symbol selection dialog. You can combine --symbols with a scheme:

./gns3theme.py -s nord --symbols

How it works

gns3theme patches the GNS3 GUI to add a Custom interface style option:

1. CSS stylesheet is generated from the color scheme and saved to ~/.config/gns3theme/custom_style.css
2. Runtime config (grid color, link color, label color, console color) is saved to ~/.config/gns3theme/config.json
3. GNS3 source files are patched to:
   • Add "Custom" to the interface style list
   • Load the CSS and config when "Custom" is selected
   • Apply theme colors to canvas links and console text

Backups

Original files are always backed up to ~/.config/gns3theme/backups/ before patching. On macOS, the original GNS3.app is preserved as /Applications/GNS3.app.bak. Backups are never deleted.

Restore

# Restore original files (auto-detect)
sudo ./gns3theme.py --restore

# Restore with explicit path
sudo ./gns3theme.py --restore /path/to/site-packages

Supported installations

Platform	Install method	Detection
macOS	GNS3.app (DMG)	/Applications/GNS3.app
macOS	pip / brew	python3 -c "import gns3" or scans site-packages
Linux	pip	~/.local/lib/pythonX.Y/site-packages
Linux	system package	/usr/lib/pythonX.Y/site-packages
Linux	pipx / virtualenv	Scans common venv paths

If auto-detection fails, specify the path manually with --gns3-dir.

Requirements

• Python 3.8+
• GNS3 GUI installed

No additional Python dependencies are required.

License

MIT