How to Use the Text Diff Checker
- Paste your original text: Enter the first version of your text in the left textarea. This can be code, configuration files, documents, or any plain text.
- Paste the modified text: Enter the second version in the right textarea. The tool compares both versions line by line.
- Click Compare: The diff engine instantly analyzes both texts and displays a side-by-side comparison. Added lines are highlighted in green, removed lines in red, and unchanged lines appear in muted color.
- Review the statistics: A summary bar shows the number of lines added, removed, and unchanged, giving you a quick overview of how much the text has changed.
- Use Swap or Clear: Click Swap to reverse the original and modified texts, or Clear to start fresh with new content.
Understanding Text Diffing Algorithms
The text diff checker uses the Longest Common Subsequence (LCS) algorithm, a classic computer science approach for comparing sequences. The algorithm finds the longest sequence of lines that appear in both texts in the same order, then uses this to identify which lines were added, removed, or left unchanged. The LCS approach is the same one used by the Unix diff command and version control systems like Git, making it a battle-tested method for identifying changes between document versions.
Diff tools are essential in software development for code reviews, debugging, and version control. When a developer modifies source code, a diff viewer shows exactly which lines changed, making it easy to spot bugs introduced by recent edits or to review a colleague contributions. But diffing is equally valuable outside of programming — writers use it to track revisions in manuscripts, lawyers use it to compare contract versions, and data analysts use it to identify changes in structured data files.
This tool performs all comparisons entirely in your browser, meaning your data never leaves your computer. This is particularly important when comparing sensitive documents like legal contracts, confidential business plans, or proprietary source code. The line-by-line comparison provides a clear visual representation of changes without requiring any software installation or account creation.