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Introduction

Litmus test your terminal themes — preview them across all your apps before you commit.

Litmus Try it live at litmus.edger.dev

The Problem

Switching terminal themes is a frustrating loop:

  1. You find a theme that looks nice in a preview
  2. You edit configs for kitty, wezterm, neovim, zellij, delta…
  3. You discover git diff is unreadable, or cargo warnings blend into the background
  4. You revert everything and try the next theme
  5. Repeat

The core issue: you can’t see how a theme actually looks across your real workflow until after you’ve fully set it up. A terminal’s built-in theme preview shows color swatches, but that doesn’t tell you whether a git diff or a cargo build will be readable. The decision is visual, but the evaluation process is mechanical and slow — especially on NixOS where config changes require a home-manager rebuild.

The Solution

A web app that lets you preview any theme across realistic terminal scenarios instantly — before touching a single config file.

Pick a theme. See exactly how git diff, cargo build output, bat syntax highlighting, and more will look across different terminal emulators. Litmus captures real screenshots from real terminals, so what you see is exactly what you’d get.

What’s In the Box

  • 58 themes across 30+ families (Catppuccin, Tokyo Night, Gruvbox, Dracula, Nord, Rose Pine, and many more)
  • 13 fixtures simulating real terminal output (git diff, cargo build, bat, ripgrep, shell prompt, ls, htop, and more)
  • 2 providers — kitty and wezterm, with real per-provider screenshots
  • Side-by-side comparison of any two themes
  • Accessibility tooling — WCAG contrast checking, APCA readability scoring, color vision deficiency simulation (protanopia, deuteranopia, tritanopia)
  • Config export — generate kitty.conf, TOML, or Nix attribute set for any theme

How It Works

Litmus captures real terminal screenshots by running actual commands in headless terminal emulators, then serves them through a web app where you can browse, compare, and evaluate themes. It also parses the ANSI output from those same commands to provide simulated rendering — enabling features like contrast analysis and CVD simulation that can’t work on raster images alone.

Read The Model to understand the conceptual framework that makes this work.