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Text Diff Checker

100% Free

Side-by-side line diff between two blocks of text using LCS — added/removed/equal hunks, similarity percentage, ignore-whitespace + ignore-case toggles.

LCS algorithm
Client-Side
Similarity %
Added
+0
Removed
−0
Similarity
100%
Status
Identical
Line-by-line diff
Paste text in both panes to see the diff…

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<iframe
  src="https://tools.town/embed/text-diff-checker/"
  width="100%"
  height="600"
  style="border:none; border-radius:12px;"
  loading="lazy"
  title="Text Diff Checker">
</iframe>

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How to Use

  1. 1 Paste original text on the left, modified text on the right
  2. 2 Diff updates instantly with LCS-based line matching
  3. 3 Toggle 'Ignore whitespace' or 'Ignore case' for noisy comparisons
  4. 4 Added lines highlighted green, removed red, unchanged grey

Features

  • Longest Common Subsequence algorithm (correct line matching)
  • Side-by-side diff view with line numbers
  • Similarity percentage based on common-line ratio
  • Ignore-whitespace mode for code/config diffs
  • Ignore-case mode for prose comparisons
  • 100% client-side — handles thousands of lines in-browser

Why it Matters

Spotting differences between two texts by eye is error-prone. A line-level diff with proper LCS matching highlights exactly what changed — added, removed, or moved. Useful for proofreading edits, comparing config files, and tracking changes across draft versions.

★★★★★

Use Cases

Config Diff

Compare two .env or YAML files to spot the changed setting

Editing Review

See exactly what an editor changed in a draft

Compliance Check

Detect unauthorised modifications between document versions

Frequently Asked Questions

What's LCS?
Longest Common Subsequence — the standard algorithm for line-based diffs. It finds the longest sequence of lines present in both texts, then marks the rest as added/removed. Same algorithm `diff` uses on Linux.
Why doesn't it show character-level diffs within a line?
This tool is line-granular by design — fast, easy to read for most use cases. For character-level diffs we recommend Meld, VS Code's diff view, or a dedicated word-diff tool.
How big can the inputs be?
LCS is O(n × m) memory. Up to ~5,000 lines per side runs smoothly. For larger diffs use a CLI like `git diff` or Myers' algorithm via npm.
Why is similarity 50% when only one line differs?
Similarity = common lines ÷ max(length). If both have 4 lines but 1 differs, common = 2 (because the differing pair is one removed + one added, not 'modified'), max = 4, so 50%.
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Want to go deeper?

Browse all guides →
How to Use Text Diff Checker
diff

How to Use Text Diff Checker — Complete Guide

Learn how to compare two text blocks and highlight exactly what changed using Tools.Town's free Text Diff Checker.

8 May 2026

5 min read

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