DIFF CHECKER (TEXT & CODE COMPARISON)

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Diff Checker

Compare two blocks of text or code side by side and see exactly what changed, line by line.

Added Removed

How this tool works

This tool uses the Longest Common Subsequence (LCS) algorithm — the same core technique behind tools like diff and Git's line comparisons — to find the largest set of lines that appear unchanged in both versions, then works out everything else as an addition or a removal around that shared backbone. This produces a genuinely minimal, accurate diff rather than a naive line-by-line comparison, which would incorrectly flag every line as changed the moment a single line is inserted near the top.

Lines that match exactly are shown in plain text; anything only in the "Modified" version is highlighted green as an addition, and anything only in the "Original" is highlighted red as a removal. Line numbers on the left refer to the original document's line positions where applicable.

Frequently asked questions

Does this compare word-by-word or just line-by-line?
Line-by-line. If a single word changes in an otherwise identical line, the whole line will show as one removal and one addition rather than highlighting just the changed word — this keeps the comparison fast and predictable for any size of text.

Can I use this to compare code, not just plain text?
Yes — it works on any text content, including source code in any programming language, config files, or markup. It's whitespace-sensitive, so reformatted code with different indentation will show as changed even if the logic is identical.

Why does moving a block of text show as both a removal and an addition, rather than "moved"?
This tool detects insertions and deletions, not block moves specifically — a paragraph moved to a different position will typically show as removed from its old spot and added at its new one, which is standard behavior for line-based diff tools.

Is my text sent anywhere to be compared?
No. The entire comparison runs in your browser using JavaScript — nothing is uploaded to a server.

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