For developers who spend most of their day in a terminal, context switching to a web browser or a heavy GUI application for code review is a constant drag on productivity. The standard git diff command is fast but often unreadable for anything more than a few lines. Lumen, a TUI (Terminal User Interface) written in Rust, steps directly into this gap, aiming to provide a powerful, interactive review experience without ever forcing you to leave the command line.
A Superior Diff Viewer at its Core
The main attraction of Lumen is its visual diff viewer, and it absolutely delivers. Invoked with a simple lumen diff, it transforms the standard wall of red and green text into a clean, side-by-side interface. Because it's a self-contained Rust binary, it's incredibly fast, living up to its claim of staying "snappy on multi-thousand-line diffs." The interface is enhanced with tree-sitter for accurate syntax highlighting and supports a dozen popular color themes, from Dracula to Solarized, which can be configured to match your terminal setup.
Where Lumen truly shines is in its deep integration with common developer workflows. It can diff uncommitted changes, specific commits (HEAD~1), or entire branches (main..feature/A). The standout feature here is its ability to review GitHub Pull Requests directly. Running lumen diff --pr 123 or even just passing the PR's URL fetches the changes and presents them in the same slick interface. You can even mark files as viewed with the spacebar, and that status syncs back to GitHub, a thoughtful touch that bridges the gap between local review and the remote platform.
For those who practice stacked-commit development (common with tools like git rebase -i or Jujutsu), the --stacked mode is a game-changer. It allows you to review a series of commits one by one, navigating forward and backward while the tool preserves your progress by tracking which files you've already viewed in each commit. This is a professional-grade feature that shows a deep understanding of modern Git workflows. Quality-of-life features like a watch mode (--watch), the ability to open a file directly in your editor (e), and a system for adding local annotations round out the core experience, making it feel less like a script and more like a proper application.
The Optional AI Co-pilot
Beyond the diff viewer, Lumen bundles a suite of optional AI features that can be activated by configuring an API key. These tools address common, time-consuming tasks. The lumen draft command analyzes your staged changes and generates a conventional commit message. This is more than a simple summary; adding context with lumen draft --context "..." can produce surprisingly nuanced and accurate messages.
lumen explain does the reverse, providing a natural-language summary of what a commit or set of changes does. This is invaluable for getting up to speed on a colleague's PR or deciphering a section of legacy code. You can even ask it specific questions, like lumen explain --query "What's the performance impact?".
Perhaps the most ambitious feature is lumen operate, which translates natural language into Git commands. Asking it to "squash the last 3 commits into 1" generates the correct git reset and git commit sequence. Crucially, it explains what the command does, warns about potentially dangerous operations, and prompts for confirmation before executing, providing a vital safety net.
Rough Edges and Limitations
Lumen is excellent, but it's not a complete replacement for a web-based review platform. Its biggest limitation is that the annotation feature is entirely local. You can add comments to lines, hunks, or files for your own reference, but you can't share them or engage in a threaded discussion with teammates within Lumen itself. The workflow is to review in Lumen, then switch to the GitHub UI to leave comments. This is a reasonable trade-off, but one to be aware of.
As a TUI, it is keyboard-driven and will feel alien to those who rely on a mouse and graphical buttons for everything. It's an opinionated tool for an opinionated workflow. Finally, while its core dependencies are minimal, getting the most out of it (e.g., the interactive lumen explain --list) requires optional tools like fzf, which may be an extra installation step for some.
Community and Where It Fits
The project appears healthy and actively maintained. With over 2,600 stars and a manageable 64 open issues, there's clear user adoption and engagement. The release of v2.32.0 in mid-July 2026 shows a consistent development cadence, giving confidence that the tool is not abandonware.
In a real-world stack, Lumen serves as a powerful enhancement to a developer's local environment. It replaces raw git diff for day-to-day work and acts as a "first pass" tool for reviewing pull requests with speed and focus. The AI features can be integrated to streamline the commit and code-comprehension process. It doesn't replace the collaborative hub of GitHub or GitLab, but it makes the individual developer's contribution to that process faster, more pleasant, and more powerful.