Diff Checker
Paste an original version and a changed version of any code or text, then compare them line by line. Removed lines are highlighted in red, added lines in green — all calculated locally in your browser.
How to Use the Diff Checker
- Paste the original version of your code or text into the left box.
- Paste the updated/changed version into the right box.
- Click "Compare" to run a line-by-line comparison.
- Lines removed from the original are shaded red in the left result panel; lines added in the changed version are shaded green in the right result panel. Lines that appear in both are shown unhighlighted.
Why Use This Tool?
Is my code or text uploaded anywhere?
No. The entire comparison runs inside your browser using JavaScript — nothing you paste is sent to a server, logged, or stored. This makes it safe to compare proprietary source code, configuration files, contracts or any sensitive text without worrying about data leaving your device.
How does the comparison algorithm work?
The tool splits both inputs into individual lines and runs a longest-common-subsequence (LCS) based line-matching algorithm — the same core idea used by tools like diff and Git's line-level diffing. Lines that exist unchanged in both versions are matched and left plain; anything only in the original is marked as removed, and anything only in the changed version is marked as added.
Can I compare full source code files, not just plain text?
Yes. The comparison is language-agnostic and works on any plain-text content — JavaScript, Python, HTML, JSON, config files, log output, or ordinary prose. Because it works line by line, formatting differences like re-indented blocks may show more changed lines than a semantic code diff, so it's best suited for spotting textual changes rather than deep AST-level code analysis.
Who uses a diff checker?
Developers reviewing a colleague's code changes outside of Git, writers comparing two drafts of an article, and QA testers checking whether a configuration file changed between deployments all rely on a fast visual diff to catch what's different without reading every line manually.