Diff Checker

Professional line-by-line text comparison. Secure, private, and precise.

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Original
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Modified
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How Text Comparison Works

The Diffing Algorithm

The Diff Checker uses an advanced string comparison algorithm to analyze two blocks of text side-by-side. It identifies the Longest Common Subsequence (LCS) to determine exactly which characters, words, or lines have been added, deleted, or modified between the original and modified texts.

Zero-Server Privacy

Unlike many online diff checkers that upload your documents to an external server for processing, our Diff Checker runs entirely locally in your browser. Whether you are comparing confidential legal contracts or proprietary source code, your data remains 100% private.

Diff Checker — Help & FAQ

How does the comparison work?

We use a line-by-line diff algorithm. Every line in the original text is compared against the modified text. Lines that exist only in the original are marked removed (red), lines that exist only in the modified version are marked added (green), and unchanged lines are shown as-is.

Is my text sent to a server?

No. Everything runs 100% in your browser using JavaScript. Your text is never uploaded, stored, or transmitted anywhere. This tool is completely private.

What about very long lines?

Long lines are handled with horizontal scrolling in each diff pane. Both panes scroll in sync, so when you scroll right in one pane the other follows. You can also scroll both panes vertically in sync.

Can I compare code?

Yes, any plain text works — code, prose, JSON, CSV, config files, anything. For best results with code, make sure indentation is consistent between the two versions.

What does the Clear button do?

Clicking Clear wipes both text input fields and resets the diff result back to the empty state. This is faster than manually selecting and deleting text from both boxes.