Text Diff Checker

The Text Diff Checker is a free online tool that compares two blocks of text and highlights every difference between them. It uses a Longest Common Subsequence (LCS) algorithm to perform line-by-line comparison and detect added, removed, modified, and unchanged lines.

Features

• Line-by-line comparison using LCS diff algorithm
• Character-level highlighting within modified lines
• Side-by-side and unified diff view modes
• Ignore whitespace differences option
• Case-insensitive comparison toggle
• Statistics showing added, removed, modified, and unchanged lines
• Copy diff output in standard diff format
• Swap texts and sample text loading

Common Use Cases

• Code review: Compare two versions of source code to spot bugs or changes
• Document editing: Track changes between draft revisions of articles or essays
• Configuration files: Verify differences between server configurations or environment files
• Data validation: Compare CSV or JSON exports to detect discrepancies
• Translation review: Compare original and translated texts side by side
• Legal documents: Identify changes between contract versions or policy updates

How It Works

This tool splits both texts into lines and runs a Longest Common Subsequence (LCS) algorithm to find the optimal alignment. Lines present only in the original are marked as removed (red), lines present only in the modified text are marked as added (green), and consecutive remove-add pairs are detected as modified lines (yellow) with character-level diff highlighting. All processing happens in your browser -- no data is sent to any server.