Text Diff Checker: compare text differences instantly

Paste the original and modified versions of your text to instantly see additions and deletions. Everything runs in your browser: your text never leaves your device.

Original text 0 lines
Modified text 0 lines
Private by design. Your text is processed only in this browser using pure vanilla JavaScript. Nothing is uploaded and no external libraries are used.
About this tool

How to use the Text Diff Checker

  1. 1
    Paste original text Paste the original version of your text into the left box.
  2. 2
    Paste modified text Paste the modified version of your text into the right box.
  3. 3
    Compare Press the Compare button to instantly see the differences highlighted line by line.

Special features

Line-by-line comparison Instantly see exactly which lines were added, removed, or left unchanged.
Visual highlights Added text is highlighted in green, and removed text is highlighted in red for easy reading.
100% private Your text never leaves your browser. No uploads, no servers, no tracking.
Code-friendly Perfect for comparing source code, CSVs, configuration files, and plain text.
Fast & lightweight Built with an optimized algorithm that runs instantly without relying on external servers.
Offline capable Because the tool is built entirely with vanilla JavaScript, it works completely offline after the page loads.

Frequently asked questions

How does the diff algorithm work?

The tool uses a Longest Common Subsequence (LCS) algorithm. It breaks both texts down into lines and calculates the most efficient sequence of additions and deletions required to transform the original text into the modified text.

What do the colors mean?

Lines with a green background and a plus sign (+) represent text that was added in the modified version. Lines with a red background and a minus sign (-) represent text that was removed from the original version.

Can I compare code?

Yes. The tool compares text line by line, making it perfect for comparing source code, CSV files, or configuration files.

Is my text safe?

Yes. Your text is processed entirely in your browser. It is never uploaded, stored, or sent anywhere. The tool does not use cookies, analytics, or localStorage.

Does the tool work offline?

Yes. Because the tool is built entirely with vanilla JavaScript, it works completely offline after the page loads.