Diff Checker
Compare two blocks of text line by line and see exactly what was added and removed.
Compare two texts line by line
The Diff Checker compares two blocks of text and highlights exactly what changed — additions in green, removals in red, with unchanged lines in between. Paste an original and a revised version and instantly see the differences, with a count of lines added and removed. It runs entirely in your browser, so your text stays private.
How it works
The tool uses a longest-common-subsequence algorithm — the same approach behind git diff and code review tools — to find the smallest set of changes that turns the original into the revised version. That produces a clean, accurate diff that aligns matching lines and only flags what truly changed, rather than marking everything after the first edit.
How to use it
- Paste the original text on the left.
- Paste the changed text on the right.
- Review the highlighted differences below.
What the colors mean
| Marker | Meaning |
|---|---|
| + green | Line added in the changed version |
| − red | Line removed from the original |
| grey | Unchanged line |
Common uses
- Code review — see what changed between two versions.
- Document editing — compare drafts of an article or contract.
- Config files — spot differences between environments.
- Proofreading — find edits between two versions of text.
Private by design
Many online diff tools send your text to a server. This one compares everything locally in your browser, so confidential code, contracts, and documents never leave your device. There's no upload and no account required.
Private and free
The tool is completely free with no sign-up and no limits on text size.
Frequently asked questions
How does the diff work?
It uses a longest-common-subsequence algorithm to find the minimal set of line additions and removals between the two texts.
Does it compare word by word?
It compares line by line, which is ideal for code and documents. Each changed line is shown as removed and added.
Is my text uploaded?
No. The comparison runs entirely in your browser and nothing is uploaded.
Is it free?
Yes, completely free with no sign-up.