About DiffMate
DiffMate is a free big data diff tool that compares CSV and Excel files with 1,000,000+ rows right in your browser. Powered by a Web Worker engine and virtual scrolling, the UI never freezes — even with 68 MB files. Zero server uploads ensure complete privacy.
Our Mission
Everyone should be able to compare documents easily and safely. You shouldn't need to buy expensive software or upload sensitive files to unknown servers. DiffMate was built to solve this problem.
How Does It Work?
- You select files in your browser.
- A JavaScript engine parses the files (SheetJS for XLSX, pdf.js for PDF).
- Files are compared using an LCS (Longest Common Subsequence) algorithm.
- Differences are visualized with colors and character-level highlighting.
- The entire process completes within your browser. Zero network communication.
Tech Stack
React + TypeScript + Vite
SheetJS (XLSX), pdf.js (PDF), TextDecoder (TXT/CSV)
LCS-based SequenceMatcher (ported from Python difflib)
Web Worker background thread, line interning, virtual scrolling for 1M+ rows
Static site hosting ($0 server cost)
Why Choose DiffMate
Complete Privacy
Your files never leave your browser. Open the network tab to verify — no file data is sent externally.
Completely Free
All features available for free, no hidden fees or premium tiers. No registration required.
Big Data Performance
Tested with 68 MB CSV and million-row Excel files. Web Worker engine runs diff in a background thread so the UI never freezes.
Multilingual
Supports Korean, English, and Chinese. Automatic encoding detection handles files in various languages.
No Installation
Use anywhere with just a web browser. No app installation, plugins, or registration needed.
Bidirectional Editing
Copy changes between sides to merge documents. Modified files can be downloaded immediately.
Use Cases
Contract Review
When you receive a revised contract, precisely identify which clauses were changed.
Code Review
Quickly review source code changes and examine team members' modifications.
Big Data Migration Validation
Compare CSV/Excel files with 1M+ rows before and after migration to verify data integrity. Detects changes down to the cell level.
Document Versioning
Track revision history of reports and proposals, precisely identifying changed sections.