difit: GitHub-Style Local Diff Viewer with AI Code Review

AI coding agents have made writing code faster. But what about reviewing it? Terminal git diff shows line-by-line text diffs, and once you’re dealing with more than 10 changed files, keeping track of every detail gets tricky. Pushing to GitHub and opening a PR makes things easier to read — but sometimes you want to review changes locally before pushing.

difit is a CLI tool that solves exactly this. It displays your local git diff in a GitHub-style web viewer, lets you add comments to any line of the diff, and generates AI agent prompts from those comments with a single click.

How difit Works: Architecture and Tech Stack

difit is an open-source CLI tool developed by yoshiko-pg. Running npx difit starts an Express-based local server (default port: 4966) and opens a GitHub-style UI in your browser, built with React 18, TypeScript, and Tailwind CSS v4.

Comparison with Traditional Diff Tools

Feature	git diff	GitHub PR	difit
Setup steps	0 steps	2 steps	1 step
UI	Text	Browser	Browser (GitHub-style)
Comments	No	Yes	Yes
AI prompts	No	No	Yes
Offline	Yes	No	Yes

difit’s position is clear: it combines the convenience of git diff with the readability of GitHub PRs, and adds AI prompt generation as its unique feature.

Installation and Setup

npx difit        # Run immediately, no install needed
npm install -g difit  # For global installation

Flexible Diff Display Options

difit supports a variety of diff display modes. You can choose the right argument for each situation.

difit              # Show diff for the HEAD commit
difit .            # All uncommitted changes (staged + unstaged)
difit staged       # Staged changes only
difit working      # Unstaged changes only
difit @ main       # Compare HEAD with the main branch
difit . origin/main  # Compare working directory with remote main

It also accepts unified diff from stdin.

git diff --merge-base main feature | difit

difit also supports GitHub PR review. If you’ve already run gh auth login, authentication is handled automatically.

difit --pr https://github.com/owner/repo/pull/123

Choosing the Right Argument

If an AI agent has just finished an implementation, difit . origin/main is your best option — it shows all changes relative to remote main, regardless of commit status. If you want to review only staged changes before committing, use difit staged. To review a specific PR locally, use difit --pr {URL}.

I personally use difit staged and difit . origin/main as custom commands in my daily workflow. Checking staged diffs before creating a PR has become a habit — a quick sanity check to make sure no unintended changes have slipped in. Since I’m already used to the GitHub UI, being able to review in the same familiar interface is a real advantage.

AI Prompt Generation: How Line Numbers Improve Fix Accuracy

difit’s standout feature is the integration between its comment system and AI prompt generation.

Converting Comments to Prompts

Click any line in the diff to add a comment. The “Copy Prompt” button generates a prompt combining the file path, line number, and comment content. “Copy All Prompt” collects all comments into a structured format for copying at once.

Here’s an example of a generated prompt.

src/components/Button.tsx:L42-L48
This logic is missing a null check.
Please handle the case where props.onClick is undefined inside handleClick.

The file path, line range, and fix description are bundled into one. This format works with any AI tool.

Why Line Numbers Improve AI Fix Accuracy

This was the part that surprised me most. When you use difit to generate prompts with line numbers, the accuracy of AI fixes is noticeably higher compared to describing the problem in plain text alone.

Here’s a structured breakdown of why.

Instruction Method	Prompt Example	AI Processing
Text only	”Null check is missing”	Guesses the target → risk of misidentification
With line numbers	Button.tsx:L42-L48 + comment	Immediately identifies target → accurate fix

With text-only instructions, the AI has to guess which function “click handler” refers to. When there are multiple functions or event handlers with similar names, there’s a risk of modifying the wrong part of the code.

With coordinates like L42-L48, the AI can read the target code directly. It’s an approach that compensates for the ambiguity of natural language with structured positional information. You can manually type line numbers like L42-L48, but difit lets you click a line in the diff and fills them in automatically — that’s where the real convenience lies.

Practical Workflow: Self-Review Cycle Before a PR

Here’s the workflow I use in my daily practice.

Currently, I use AI agents from remote, GitHub, and local interfaces, switching my starting point depending on the task. I use difit when working locally. After creating a Pull Request on GitHub, I interact with AI agents there — but when work comes back to local, I’ll reach for difit again.

The AI Agent Feedback Cycle

1. Ask an AI agent to implement something
2. Run difit . origin/main via a custom command to review the diff in a GitHub-style UI
3. Click lines of interest and add review comments
4. Click “Copy All Prompt” at the top of the screen to copy the prompt
5. Paste the copied prompt to the AI agent and request fixes
6. After the fix is complete, review the diff with difit again
7. If everything looks good, run git push and create a PR

The key to this cycle is that reviewing and generating fix instructions happen entirely within difit. By ensuring quality locally before pushing to GitHub, you reduce the back-and-forth in PRs.

Comment Persistence

difit saves comments to the browser’s localStorage per commit. Even after closing the browser, reopening difit with the same arguments restores your previous comments. When you close the browser, the comment content is also printed to the terminal, so there’s no risk of losing your notes.

Limitations and Constraints

There are a few constraints worth knowing before adopting difit.

• Requires Node.js 21 or higher — Check your current version with node -v
• Rendering load with large diffs — When many files change, the browser may slow down. Lock files and generated code are mitigated by automatic folding
• No patch generation — difit is a review-focused tool; it doesn’t support patch file generation or merge functionality

Summary: Review Quality Determines Code Quality

difit addresses three key challenges in AI-era code review.

• Readability — Review intuitively with a GitHub-style UI instead of terminal git diff
• Instruction ambiguity — Line-number-aware prompts make AI fix instructions pinpoint-precise
• Workflow fragmentation — Converting comments to prompts in one click directly connects review and fixing

As AI writes more of the code, the human role is shifting toward review. difit is a strong option for improving the precision of that review.

This article is based on information available as of February 1, 2026.