Diff Checker

How to compare two texts

1. Paste the earlier version into Original and the later one into Changed.
2. Tick Ignore leading/trailing spaces if indentation differences should not count, and Ignore case if capitals should not.
3. Tap Compare. Lines only in the original are shown in red as removed, lines only in the changed version in green as added, and matching lines are left plain.

How a line diff works

The tool splits both texts into lines and finds the longest run of lines the two have in common, in the same order. Those are the unchanged lines. Whatever is left over in the original was removed, and whatever is left over in the new version was added. It is the same idea that version control systems such as Git use to show changes.

Because the unit is the line, a change of one word shows as one line removed and one line added. That is correct: the old line is gone and a new one took its place.

Getting a clean comparison

• Break long paragraphs up. If a whole paragraph is a single line, any edit marks all of it. Put each sentence on its own line in both versions first, and the diff will point to the sentence that changed.
• Format structured data the same way. Run both versions of a JSON document through the JSON Formatter with sorted keys before comparing. Otherwise spacing and key order hide the real change.
• Use “Ignore spaces” for code that has only been re-indented, and for text pasted from a PDF or an email, which often carries stray spaces at line ends.
• Watch for invisible differences. Curly and straight quotes, tabs and spaces, and non-breaking spaces look alike on screen but count as changes.

What people compare

• Contract and policy drafts — to see what the other side changed before you sign.
• Configuration files — to find why one server behaves differently from another.
• Code snippets — when a full version control tool is not to hand.
• Essays and articles — an edited draft against the original.
• Exported lists — yesterday's and today's, to see which rows appeared or disappeared. Sort both first.

Privacy and limits

The comparison runs in your browser and neither text is uploaded, which makes it suitable for contracts, credentials in a config file and unreleased code. Very long texts of many thousands of lines take longer, because every line of one is weighed against the other. For checking length rather than differences, use the Word Counter.