Is my text sent to any server?

No. All comparison logic runs entirely in your browser using JavaScript. Nothing is transmitted or stored externally.

What algorithm does this use?

It uses a Longest Common Subsequence (LCS) algorithm, which is the same family of algorithms used by Unix diff and Git. It finds the minimal set of additions and deletions to transform the original text into the modified text.

Does it handle large files?

Yes, for typical use cases such as config files, code snippets, or documents. Very large files (thousands of lines) may take a moment since the LCS algorithm is O(n*m) in complexity.

Are whitespace-only lines treated as changes?

Yes. Each line is compared exactly as typed, including leading and trailing spaces. This matches the behavior of standard diff tools.

Can I use this to compare code?

Absolutely. The tool works on any plain text — source code, JSON, YAML, SQL, prose, or anything else you can paste.

Diff Checker

Name: Diff Checker
Availability: InStock
Author: Nham Vu

Paste two blocks of text and instantly see which lines were added, removed, or unchanged — color-coded for clarity.

Original

Modified

Paste text in both boxes, then click Compare.

Copied!

Summary

Paste two blocks of text and instantly see which lines were added, removed, or unchanged — color-coded for clarity.

How it works

Paste the original text into the left box and the modified text into the right box.
Click Compare. A Longest Common Subsequence (LCS) algorithm — the same family Unix diff and Git use — finds the minimal edit path between the two sides.
Each line is classified as added, removed, or unchanged, then color-coded with a + or - prefix.
Read the green (added) and red (removed) lines, check the change counts, and copy the result as plain text.

Use cases

Compare two versions of a configuration file before deploying.
Review code patch changes before applying them.
Check what changed between two drafts of a document or essay.
Spot unwanted modifications in log files or data exports.
Validate that a copy-paste preserved all expected lines.

Frequently Asked Questions

Last updated: 2026-06-09 · Reviewed by Nham Vu