Text Diff Checker
Compare two blocks of text and see added, removed, and unchanged lines — line-level LCS diff, 100% client-side.
Frequently Asked Questions
How does the text diff checker work?
It runs a line-based LCS (longest common subsequence) algorithm in your browser to find the longest matching sequence of lines. Anything not in that sequence is marked as added or removed.
Is my text uploaded anywhere?
No. All processing is 100% client-side in vanilla JavaScript. Your text never leaves your device.
What's the difference between line-level and character-level diffs?
Line-level compares whole lines as units, which is faster and matches how Git and most code review tools display diffs. Character-level highlights individual characters.
Can I diff code files?
Yes. Paste the old and new versions of any plain text — source code, config, markdown, or logs.
Is there a size limit?
No hard limit, but LCS is O(n*m). Keep each side under a few thousand lines for instant results.