Diff Checker
Compare two blocks of text and see exactly which lines were added, removed or left alone.
How to use this tool
- Fill in the options above.
- The result updates as you change the input — there is nothing to submit and nothing to wait for.
- Read the figures in the result panel.
- Use Copy or Download if you need the output elsewhere. Nothing was uploaded at any point.
The comparison runs line by line using a longest-common-subsequence match, which is what git and most code review tools use. Added lines are marked with +, removed lines with -, and unchanged lines are kept for context so you can see where a change sits. Whitespace and case can be ignored, which matters when the only difference is indentation.
Diff Checker — the specification
| Granularity | Line by line, with unchanged lines kept as context |
|---|---|
| Method | Longest common subsequence |
| Options | Ignore whitespace, ignore case |
| Output | Unified diff you can download |
How it works
This tool runs entirely in your browser. There is no server involved, which means nothing you type or upload is transmitted, stored, or logged — and there are no usage limits, because there is nothing for us to ration.
You can confirm it yourself: open your browser's developer tools, select the Network tab, and use the tool. No request is made.
Who needs Diff Checker
Checking what changed between two drafts of a contract, comparing a config file against a backup, or finding the one altered line in a block of code someone pasted you.
Diff Checker — frequently asked questions
Does it compare word by word or line by line?
Line by line. Character-level diffs look impressive but are harder to act on, and they turn a single reworded sentence into a confusing mess of fragments. If a line changed at all, you see the old one and the new one.
Why does it say lines were added and removed when I only edited one?
A changed line is shown as one removal and one addition, because that is what it is at line level. Two counts of one, on adjacent lines, usually means a single edit.
Is there a size limit?
Comparison cost grows with the product of the two line counts, so very large files are refused rather than freezing your browser. Compare a section at a time if you hit that.
Does this work offline?
Yes. Once the page has loaded you can disconnect from the internet and it keeps working, because all the processing happens in your browser. That is also the simplest way to confirm nothing is being sent anywhere.
Can I use this on a phone?
Yes. The layout adapts to a small screen and everything works the same way.
Is this tool really free?
Yes. No account, no trial period, no watermark on the output and no cap on how many times you use it. The site is funded by advertising.
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Background reading: Text and Developer Tools That Never Upload Your Data
Your file never leaves your device. Open your browser's Network tab while you use this page and you will see no upload — how that works.
Disclaimer. Published requirements change without notice. Confirm against the official source before you submit. Full disclaimer.