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