DiffMate is a free, browser-based document comparison tool designed to help professionals find differences between two versions of any document. Whether you are comparing million-row CSV data exports, Excel spreadsheets with complex formulas, PDF contracts, or plain text configuration files, DiffMate processes everything directly in your browser — no files are ever uploaded to a server.

Comparison Algorithm

DiffMate uses an advanced sequence matching algorithm based on Python's well-established difflib SequenceMatcher. This algorithm identifies the longest common subsequences between two documents, then precisely highlights what was added, removed, modified, or moved. For large datasets such as CSV and Excel files with hundreds of thousands of rows, the comparison runs inside a Web Worker — a separate background thread — so your browser interface remains fully responsive throughout the entire process.

100% Client-Side Processing

Unlike cloud-based comparison tools that require you to upload sensitive documents to remote servers, DiffMate runs entirely within your browser's sandbox environment. Your files are read using the browser's File API, parsed locally, and compared using JavaScript. No data is transmitted over the network, making DiffMate ideal for confidential documents, proprietary data, financial records, and any files subject to data protection regulations such as GDPR or HIPAA.

Supported File Formats

DiffMate supports four major document formats: plain text files (.txt), comma-separated values (.csv) with automatic encoding detection supporting UTF-8, EUC-KR, ISO-8859-1, and UTF-16, Microsoft Excel spreadsheets (.xlsx, .xls) parsed using the SheetJS library, and PDF documents (.pdf) with text extraction powered by Mozilla's pdfjs-dist engine. The tool automatically detects file encoding using a multi-step cascade: BOM detection first, then sequential encoding attempts to ensure accurate character display regardless of the file's origin.

Who Uses DiffMate?

DiffMate is used by data analysts comparing database exports, accountants auditing financial spreadsheets, legal professionals reviewing contract revisions, IT teams tracking configuration changes, and quality assurance engineers validating test output files. With support for files up to 68 MB and over 1 million rows, DiffMate handles real-world enterprise-scale document comparison tasks that other browser-based tools cannot.