How I Built a Lightweight Diff Tool with Unlimited Merge - Diff Guru

#react #nextjs #webdev #productivity

If you’ve ever tried to compare two large files - say, two JavaScript files with 5,000+ lines, you know the pain.
Scrolling endlessly just to find the actual differences can be frustrating and time-consuming.

I faced this problem regularly while working on client projects and code reviews, which led me to create DiffGuru.com - a lightweight, privacy-first diff and merge tool built with React and Next.js that runs entirely in the browser.

The Problem

Most online diff tools work well for small files but start lagging or freezing with large datasets.
Some even send your data to external servers for processing - which is a privacy red flag when working with confidential code or documents.
And Some are allowed limited merge features.

I wanted a tool that was:

Fast and lightweight
Works entirely in the browser
Supports unlimited merge
Protects user privacy - no data leaves the device
Dark and Light Theme

The Solution: Browser-Based Diff Engine

The idea was simple - process everything locally in the user’s browser using JavaScript.

This means:

No backend API calls
No file uploads
No data stored anywhere

All comparison logic runs inside the browser using efficient Diff Patch Match Js library

This ensures performance, even for large files.

The Unlimited Merge Feature

Most online tools limit you to comparing two files - that’s it.
But in real development workflows, we often need to merge multiple versions together (for example, merging test, staging, and production files).

That’s why I introduced Unlimited Merge - a feature that lets you:

Compare multiple versions of the same file
Merge changes from all versions into one output
Keep your entire workflow in one tab
No signup, no limits.

Privacy by Design

Privacy was a top priority from day one.

Here’s how Diff Guru keeps your data safe:

No uploads: Everything runs in your browser memory.
No logs or analytics tracking user content.
Instant clear: When you close the tab, everything is gone.

It’s perfect for developers working on private repositories, enterprise codebases, or sensitive documents.

Performance & User Experience

To make it lightning fast and smooth:

Used virtual scrolling for large files
Implemented line-level and word-level diffing
Added Next / Previous Difference navigation
Optimized rendering to avoid DOM overload

Even with 25k+ lines, the diff loads in seconds.

Built by a Developer for Developers

I built Diff Guru after struggling with existing diff tools that couldn’t handle real-world use cases.
Every feature - from local processing to unlimited merging - was designed with developer pain points in mind.

The Technical Stack

Frontend Framework: React
Framework for Optimization & SEO: Next.js
Diff Engine: Diff Patch Match Js library
UI Library: Tailwind CSS for simplicity and speed
State Management: React hooks

If you frequently compare logs, JSON, code, or any kind of text files, give it a try:
👉 https://diffguru.com

What’s Next

I’m working on adding: