How to compare two texts
- Paste the original in the left box and the changed version in the right box.
- Read the differences. The comparison updates as you type. Removed lines are marked with −, added lines with +, and within a changed line the exact words that differ are highlighted.
- Choose a view. Side by side puts the two versions next to each other (one above the other on a phone). Unified shows one column, like the output of
diff -uor a code review. - Copy the diff if you want to share it or apply it as a patch.
What the options do
| Option | Effect | Use it when |
|---|---|---|
| Only show changes | Hides unchanged lines, keeping 3 lines of context around each change. | Long documents with a few edits. |
| Ignore case | "Invoice" and "INVOICE" count as the same. | Only the wording matters, not capitals. |
| Ignore whitespace | Spaces and tabs are left out of the comparison. | Code that was re-indented, or text with double spaces. |
| Ignore blank lines | Empty lines are skipped on both sides. | Paragraph spacing changed but the text didn't. |
How the comparison works
The tool uses the Myers diff algorithm, the same approach behind git diff and the classic Unix diff. It finds the smallest set of lines to remove and add that turns the original into the changed text. That's why a moved paragraph shows as removed in one place and added in another: the algorithm reports edits, not moves.
When a block of removed lines is followed by added lines, they are paired up as changed lines, and a second, word-level comparison highlights exactly which words differ. A single changed number or comma is easy to spot even in a long line.
Worked example
Original: "Payment is due within 30 days." Changed: "Payment is due within 15 days." The tool reports 1 changed line and highlights only 30 → 15. The unified diff reads:
@@ -1 +1 @@ -Payment is due within 30 days. +Payment is due within 15 days.
Good uses for a diff checker
- Contracts and terms. Check what a client changed in an agreement before you sign it.
- Writing and editing. Compare two drafts of an article, essay or cover letter.
- Code and configuration. Spot the difference between two versions of a config file or a snippet. Format JSON first with the JSON formatter so the lines line up.
- Data checks. Compare two lists, such as exported email addresses or product codes, to find what was added or removed. Sorting both lists first gives a cleaner result.
Large texts
The comparison runs in your browser and waits until you pause typing, so the page stays responsive. Texts of several thousand lines compare in a fraction of a second. Each side is limited to 20,000 lines; anything after that isn't compared, and the tool tells you. If two long texts have almost nothing in common, the differing part is shown as removed and re-added rather than matched line by line.
Private: your text stays on your device
Nothing you paste is uploaded. The comparison happens in your browser, and it keeps working offline once the page has loaded. That makes it safe for contracts, private notes and code that isn't public.
Frequently asked questions
Is this diff checker free?
Is my text uploaded or saved?
What is the difference between side-by-side and unified view?
Why is a moved paragraph shown as removed and added?
Can I compare code or JSON?
Last updated . How we check our tools.