Text Diff Checker

How to Use

Paste your original text on the left and the changed text on the right. The comparison updates instantly below, marking added lines in blue with a plus and removed lines in red with a minus, while unchanged lines stay plain. A summary shows how many lines were added and removed.

Why This Tool Is Useful

Manually spotting what changed between two versions is slow and error-prone, especially in long text. A diff checker highlights the exact differences so you can review edits at a glance. It's useful for proofreading revisions, reviewing code or configuration changes, comparing contract drafts, and checking what a copy-edit changed.

How to Read the Diff

The result compares the two texts line by line. Lines that appear only in the changed version are marked as added (blue, with a +). Lines that were in the original but not the new version are marked as removed (red, with a −). Lines that are identical in both are shown unchanged.

The summary at the top counts the added and removed lines so you get a quick sense of how much changed.

How the Comparison Works

The tool uses a longest-common-subsequence (LCS) algorithm on the lines of each text — the same core idea behind developer diff tools like Git. It finds the largest set of lines that appear in both versions in the same order, then marks everything else as added or removed.

Because it compares whole lines, small changes within a line show as one line removed and one line added.

Common Uses

A diff checker helps whenever two versions need comparing:

• Proofreading — see exactly what an editor changed.
• Code and config — review edits before applying them.
• Contracts and documents — spot changes between drafts.
• Data files — find differences between two exports.

What the Markers Mean