What Is File Difference Tool?
File Difference Tool compares two text files side by side, line by line, and instantly highlights which lines match and which don't. Matching lines are shown in green, different lines in red. This tool runs 100% client-side — your files are never uploaded to any server.
It features a side-by-side split view with line numbers, drag-and-drop file loading, file upload buttons, swap functionality, diff navigation, copy and download output, and automatic data persistence across page refreshes.
How to Use This Tool
Add Your Text
Paste text into File A and File B, click the Upload button to load files, or drag and drop files onto each panel.
Compare
Click Compare. The output shows both files side by side — matching lines highlighted green, different lines highlighted red.
Navigate Differences
Use the Prev/Next buttons to jump between different lines. The counter shows your position (e.g., 3/12) in the list of differences.
Export Results
Click Copy Diff to copy the comparison to clipboard, or Download to save it as a text file. Use Swap to switch File A and File B.
Features Explained
Side-by-Side Comparison
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Both files are displayed in two equal columns with a divider between them. Each row represents the same line number in both files, making it easy to spot differences at a glance.
Line-by-Line Matching
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Line 1 of File A is compared with Line 1 of File B, Line 2 with Line 2, and so on. Matching lines are highlighted green, different lines are highlighted red.
Line Numbers
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Every row has a line number on both sides, including empty lines and blank paragraphs. Numbers are always sequential with no gaps.
Diff Navigation
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Use the Prev/Next buttons to jump between different lines. The counter shows your current position in the list of differences.
Swap Files
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Click Swap to instantly switch File A and File B. If a comparison is active, it automatically re-runs with the swapped content.
Copy & Download
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Copy the comparison output to clipboard in a unified diff format, or download it as a .txt file for sharing or archiving.
Drag & Drop
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Drop files directly onto the File A or File B panels. Each panel has its own drop zone with visual feedback.
File Upload
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Click the Upload button next to each file label to load a file from your device.
Data Persistence
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Your File A and File B content is automatically saved to your browser. Refreshing the page or returning later restores your data and re-runs the comparison.
Clear All
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Click Clear All to erase both files, the comparison output, and all saved data from your browser.
Privacy & Security
This tool runs 100% in your browser. Your files are never uploaded to any server. All comparison happens locally using JavaScript.
Your data is saved only in your browser's localStorage for persistence. No cookies, no analytics, no third-party services have access to your content. Click Clear All to remove all stored data.