What Is Text Diff?
Text Diff compares two blocks of text line by line and highlights the differences between them. Lines that were removed appear in red, lines that were added appear in green, and unchanged lines are shown in gray. It uses the Longest Common Subsequence (LCS) algorithm for accurate diff results.
This is the same type of comparison used by Git, GitHub, and code review tools. It runs entirely in your browser — no text is sent to any server.
How to Use This Tool
Enter Original Text
Paste the original version into the left panel, upload a .txt file, or drag and drop a file onto the Original area.
Enter Modified Text
Paste the modified version into the right panel, upload a file, or drag and drop. Each panel has its own Upload button.
Review Differences
The diff appears instantly below. Red lines (−) were removed, green lines (+) were added, and gray lines are unchanged.
Copy or Download
Use Copy Difference to copy the unified diff to clipboard, or Download Difference to save as a .diff file. Clear All resets both panels.
Features Explained
LCS-Based Diff Algorithm
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Uses the Longest Common Subsequence algorithm to find the optimal alignment between the two texts. This produces minimal, accurate diffs — the same approach used by professional version control systems like Git.
Large File Fallback
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For inputs over 500 lines, the tool automatically switches to a faster line-by-line positional comparison to avoid browser freezing. This trades some diff accuracy for performance on very large texts.
Unified Diff Output
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The diff is shown in a unified format with + and − markers. You can copy or download it in standard unified diff format, compatible with patch tools and code review systems.
Per-Panel File Upload
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Each panel (Original and Modified) has its own Upload button and drag-and-drop zone. This makes it easy to compare two files directly without manual copy-paste.
Who Is This Tool For?
Developers
Compare code versions, review changes before committing, or debug differences between config files.
Writers & Editors
Compare document drafts, track revisions between versions, or verify editorial changes.
QA Engineers
Compare API responses, test outputs, or configuration snapshots to detect unexpected changes.
System Administrators
Compare server configs, deployment scripts, or log files across environments.
Students
Compare assignment drafts, study notes, or code submissions to identify what changed.
Legal Professionals
Compare contract versions, policy updates, or regulatory text to identify clause changes.
Diff Legend
| Marker | Color | Meaning |
|---|---|---|
| − | Red | Line was removed from the original text |
| + | Green | Line was added in the modified text |
| (none) | Gray | Line is identical in both versions |
Tips for Comparing Text
Order matters
Put the older version in "Original" and the newer version in "Modified". This way, red lines show what was removed and green lines show what was added.
Upload files directly
Each panel has its own Upload button and drag-and-drop zone. Compare two files without opening them in a text editor first.
Download the diff
The Download button saves the diff in unified format with + and − markers. This format is compatible with patch and code review tools.
Large files use fast mode
Files over 500 lines automatically use a faster positional comparison. This may show more differences than the LCS algorithm for texts with inserted/deleted sections.
Check whitespace differences
The diff is whitespace-sensitive. A line with a trailing space is different from one without. Use Remove Extra Spaces first if whitespace differences are not relevant.
Combine with other tools
Use Sort Lines to sort both inputs before comparing to find content differences regardless of order. Use Remove Empty Lines to ignore blank line differences.
Privacy & Security
This tool runs 100% in your browser. Your text is never uploaded to any server. The diff comparison happens entirely in JavaScript on your device.
Use the “Clear All” button to remove both texts at any time. No cookies are used, no analytics track your text content, and no third-party services have access to what you type.