Text & String Tools

Text Comparison Tool

Paste two versions of a document to see exactly which lines were added, removed, or left unchanged.

Free & unlimitedRuns in your browserNo sign-up required

Original text

Modified text

+3 added−2 removed

11  The quick brown fox
2- jumps over the lazy dog
3- Hello World
2+ leaps over the lazy cat
3+ Hello TwoWorks
44  Line four
5+ Line five

How Text Diff Works

A text diff algorithm computes the minimum set of changes (insertions and deletions) needed to transform one text into another. It is the engine behind version control systems and code review tools.

The Longest Common Subsequence algorithm

Most diff tools are built on the LCS algorithm, which finds the longest sequence of lines that appear in both texts in the same order. Lines outside this subsequence are classified as additions or deletions. The unified diff format you see in git is a presentation layer on top of LCS.

Diff in version control

Every git commit stores a diff, not a full copy of changed files. This is why git repositories can store years of history with thousands of commits while remaining compact. The diff is applied forward (patch) or in reverse (revert) to reconstruct any file at any point in time.

Practical uses of text diff

Beyond code, text diff is used in legal document review to track contract revisions, in academic publishing to track manuscript edits, and in content management systems to show post revision histories. This tool works entirely in your browser with no data leaving your device.

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How it works

Three steps, no setup

Paste both versions

The original on one side, the revised version on the other.

Review the highlighted diff

Added lines are marked green, removed lines are marked red.

Focus on what changed

Unchanged lines stay neutral so edits are easy to scan.

Common questions

Frequently asked questions

What algorithm powers the comparison?

It uses the longest common subsequence (LCS) approach — the same underlying technique that powers git diff.

Does it compare word by word instead of line by line?

This tool compares at the line level, which is the clearest view for prose, config files, and code.

Keep exploring

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Text Comparison Tool

How Text Diff Works

The Longest Common Subsequence algorithm

Diff in version control

Practical uses of text diff

Three steps, no setup

Paste both versions

Review the highlighted diff

Focus on what changed

Frequently asked questions

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How Text Diff Works

The Longest Common Subsequence algorithm

Diff in version control

Practical uses of text diff