About DiffMate
DiffMate is a free, browser-based document comparison tool designed to handle enterprise-scale workloads. It compares CSV and Excel files with over 1,000,000 rows, PDF contracts, and plain text files — all within your browser. Powered by a Web Worker engine and virtual scrolling, the UI remains fully responsive even with 68 MB files. Because everything runs client-side with zero server uploads, your confidential data never leaves your device.
Our Mission
We believe that comparing documents should be easy, fast, and secure for everyone — whether you are a data analyst validating a million-row database export, an accountant auditing quarterly financial spreadsheets, or a legal professional reviewing a revised contract. Traditional comparison tools are either expensive desktop applications or cloud-based services that require uploading sensitive files to third-party servers. DiffMate eliminates both barriers: it is completely free, requires no installation, and processes everything locally in your browser. No account registration, no file uploads, no privacy risks.
How Does It Work?
- Select two files in your browser using the file picker or drag-and-drop. Supported formats include TXT, CSV, XLSX, XLS, and PDF.
- The JavaScript engine parses each file locally: SheetJS handles Excel spreadsheets, Mozilla pdfjs-dist extracts text from PDFs, and TextDecoder processes plain text with automatic encoding detection (UTF-8, EUC-KR, ISO-8859-1, UTF-16).
- For large files (100,000+ rows), parsing and comparison are offloaded to a Web Worker — a separate background thread — so the browser UI never freezes.
- The diff engine, based on Python's well-proven difflib SequenceMatcher algorithm, identifies the longest common subsequences and classifies every difference as added, removed, modified, or moved.
- Results appear in a side-by-side view with color coding and character-level highlighting. A minimap provides a bird's-eye overview of all changes across the document.
- You can copy changes between the left and right panes using arrow buttons, effectively merging the two versions. The modified file can then be downloaded instantly.
Tech Stack
React 18 + TypeScript + Vite — modern, type-safe, and fast
SheetJS (XLSX/XLS), Mozilla pdfjs-dist (PDF), TextDecoder with encoding cascade (TXT/CSV)
LCS-based SequenceMatcher faithfully ported from Python difflib, with character-level sub-diff for modified lines
Web Worker background thread, line interning for memory efficiency, virtual scrolling for 1M+ row rendering without DOM bloat
Server-side prerendering for 144 pages, 3-language support (EN/KO/ZH), structured data with JSON-LD
Cloudflare Pages static hosting — globally distributed CDN, zero server cost
Why Choose DiffMate
Complete Privacy
Your files never leave your browser. Open the Network tab in DevTools to verify — zero file data is transmitted. Ideal for confidential documents, financial records, and GDPR-sensitive data.
Completely Free
Every feature is available at no cost. No hidden fees, no premium tiers, no trial periods. We sustain the service through minimal, non-intrusive advertising.
Big Data Performance
Tested and verified with 68 MB CSV files and Excel spreadsheets exceeding 1,000,000 rows. The Web Worker engine runs the diff algorithm in a background thread, keeping the UI fully responsive throughout.
Multilingual
Full interface in Korean, English, and Chinese. Automatic encoding detection (UTF-8, EUC-KR, CP949, ISO-8859-1, UTF-16) correctly handles files from any region.
No Installation Required
Works in any modern web browser — Chrome, Firefox, Safari, or Edge. No desktop app, browser plugin, or account signup needed. Bookmark the URL and you are ready.
Bidirectional Merge Editing
Use per-line arrow buttons or bulk-apply to copy changes left-to-right or right-to-left. Download the merged result as a file when you are done.
Who Uses DiffMate?
Legal & Contract Review
Law firms and legal departments compare contract revisions to identify every changed clause, added paragraph, or deleted provision before signing.
Financial Auditing
Accountants and finance teams compare quarterly reports, balance sheets, and ledger exports to catch discrepancies and ensure accuracy.
Data Migration & QA
IT teams validate million-row CSV and database exports before and after migration, ensuring zero data loss at the cell level.
Software Development
Developers compare configuration files, test outputs, and text-based artifacts during code review and CI/CD pipelines.
Publishing & Content
Editors and content teams track changes across document versions, identifying every edit made by collaborators.
Compliance & Regulation
Compliance officers compare policy documents across revisions to ensure regulatory requirements are met without inadvertent omissions.