Online Tool Store
Diff Checker
Compare two blocks of text or code side by side with an LCS line diff, added and removed lines highlighted, and a running change count. Runs entirely in your browser.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Example shown - replace with your own code.
How the diff checker works
- Paste the original text on the left and the changed version on the right.
- The tool splits both into lines and finds the longest common subsequence of unchanged lines.
- Everything outside that subsequence is marked removed (left, red) or added (right, green), and a running +/- count is shown.
The method
A longest-common-subsequence table is built comparing every line of the original against every line of the changed text. Walking that table from the start finds the longest run of lines that appear in both, in the same order; any line not part of that run is a real edit rather than just reordering.
FAQ
What algorithm does the diff use?
A classic longest-common-subsequence (LCS) line diff, the same family of algorithm used by tools like git diff, applied line by line rather than character by character.
Can I diff any kind of text, not just code?
Yes. The comparison works on any plain text - code, config files, prose, or CSV rows - anything split into lines.
Does it highlight changes within a line, or whole lines only?
Whole lines only. A line with even a single character changed is shown as one line removed on the left and one line added on the right.
Is my code uploaded anywhere?
No. Both text panels are compared entirely in your browser tab - nothing is sent to a server.
How we compare
| Feature | Online Tool Store | Diffchecker.com | VS Code diff view |
|---|---|---|---|
| No file upload - runs in your browser | ✓ | ✗ | ✓ |
| No install required | ✓ | ✓ | ✗ |
| Free, no sign-up, no watermark | ✓ | Limited free tier | ✓ |
For a fast, private line diff without opening an editor, Diff Checker is the straightforward choice.