Diff Checker

A text diff (short for "difference") is a comparison between two versions of text that shows exactly what was added, removed, or changed. If you have ever reviewed a pull request on GitHub, tracked changes in Microsoft Word, or used the diff command in a terminal, you have already worked with diffs. They are one of the most fundamental tools in software development, writing, and document review.

At its core, a diff algorithm compares two strings and identifies the minimum set of edits needed to transform one into the other. The result is displayed with deletions highlighted in red and additions highlighted in green — a visual language that has become universal across every diff tool on the planet. SuperTextTools uses a classic longest-common-subsequence (LCS) algorithm running entirely in your browser, so your text stays private while you compare.

When do people use a diff checker?

• Code review. Before committing changes, developers compare the old and new versions of a file to make sure nothing unexpected snuck in.
• Document editing. Writers and editors compare drafts to see what changed between revisions — especially when track changes is not available.
• Config file comparison. Comparing two versions of a JSON, YAML, or .env file to spot setting changes after a deployment.
• Debugging. When output suddenly changes, diffing the old and new input helps isolate the cause quickly.
• Plagiarism and originality checks. Comparing two texts side by side to identify overlapping or copied passages.

Line vs. word vs. character comparison

Not every diff is best viewed the same way. Line mode splits text by newline and aligns rows — perfect for source code, configuration files, and multi-paragraph documents. Word mode tokenizes by words and whitespace, highlighting individual word swaps within a sentence — ideal for copy edits and legal document review. Character mode goes character by character, catching single-letter typos that line mode might bury inside an otherwise changed line.

Why use an online diff tool?

Desktop diff tools like Beyond Compare, Kaleidoscope, or even git diff are powerful, but they require installation and often struggle with quick one-off comparisons. An online diff checker is instant: paste two texts, see the result, copy or download the patch. No account, no upload, no waiting. Because SuperTextTools runs the comparison in JavaScript on your device, it works offline once loaded and never sends your content to a server — whether you are comparing proprietary source code, confidential contracts, or personal notes.