What algorithm does this use?

A classic dynamic-programming Longest Common Subsequence (LCS) line diff. It produces a minimal set of additions and deletions between the two inputs.

Does it compare word-by-word or character-by-character?

By default, line-by-line. For finer detail, run the comparison on text where each word is on its own line.

What do the line numbers mean?

The left column is the original line number, the right column is the new line number. Equal rows show both; added rows show only the new number; removed rows show only the old.

Is there a file size limit?

No hard limit, but very large inputs (millions of lines) can be slow because LCS is O(n·m). Most documents work instantly.

Is my text sent to a server?

No. The diff is computed entirely in your browser — your content never leaves your device.

Text Diff

Compare two texts line-by-line — added/removed highlighted.

100% private — no uploads Text ToolsFree & unlimited Read tutorial

See how it works

Watch a quick simulation of this tool in action — no file needed.

How to use Text Diff

Follow these steps — everything happens instantly in your browser.

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Step 1. Paste your original text in the “Old text” box.
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Step 2. Paste the changed text in the “New text” box.
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Step 3. Read the colored table: green rows are additions, red rows are deletions.
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Step 4. Use the summary badges to see how many lines were added, removed or unchanged.