Text Diff Checker
Compare two texts side by side with additions and deletions highlighted in green and red.
Compare Two Texts and Highlight Every Difference
Spotting what changed between two versions of a document by reading them both is unreliable — the eye skips over single-word edits and transposed lines. A diff does it mechanically: it computes the shortest set of insertions and deletions that turns one text into the other, then shows you exactly those.
This checker implements a longest-common-subsequence diff, the same class of algorithm behind git diff. Results are shown in aligned side-by-side panes with additions in green and deletions in red, plus optional word-level highlighting inside changed lines so you can see precisely which words moved.
Key features
- Side-by-side aligned panes — matching lines stay level so your eye can track across the change.
- Word-level highlighting — within a changed line, the specific words added or removed are marked.
- Whitespace and case options — ignore trailing whitespace or letter case to filter out noise.
- Change summary — a count of added, removed and unchanged lines at a glance.
This tool runs entirely inside your browser using native Web APIs. Your files and text are never uploaded to a server, never logged and never shared with third parties.
How to use: Text Diff Checker
- Paste the original text
Put the earlier or reference version into the left pane. - Paste the modified text
Put the newer version into the right pane. - Set comparison options
Optionally ignore case or trailing whitespace, which removes noise when comparing reformatted code. - Read the result
Green marks content only in the new version, red marks content only in the original, and unchanged lines stay neutral.
Technical specifications
| Processing location | Entirely in your browser — no server round trip |
|---|---|
| Data uploaded | None. Files and text never leave your device |
| Price | Free — no account, no trial, no usage cap |
| Category | Text |
| Works offline | Yes, once the page has loaded |
| Browser support | Chrome 90+, Edge 90+, Firefox 90+, Safari 15+ |
| Interface languages | English, 中文, हिन्दी, Español, العربية |
Frequently asked questions
Can I compare code as well as prose?
Yes. The diff is line-based and language-agnostic, so it works identically on source code, configuration files, JSON, CSV and plain prose.
How does the diff algorithm work?
It finds the longest common subsequence of lines between the two texts — the largest set of lines appearing in the same order in both. Anything outside that sequence is reported as an insertion or a deletion.
Why is a moved paragraph shown as a delete plus an add?
Classic line diffs have no concept of a move; a block that changes position appears as a removal in one place and an insertion in another. This is the same behaviour you see in standard git diff output.
Is there a size limit on the comparison?
No hard limit, though very large inputs — beyond roughly 10,000 lines each — will take noticeably longer since the algorithm is quadratic in the worst case.