Diff Checker

Free Online Diff Checker - Compare Text

Compare two texts and instantly see the differences highlighted. Our diff checker uses LCS algorithm for accurate line-by-line comparison. Shows added, removed and unchanged lines with line numbers.

Paste the original text into the left panel and the modified version into the right panel. Click compare and the tool runs a longest common subsequence (LCS) algorithm to identify line-by-line differences. Added lines appear highlighted in green, removed lines in red, and unchanged lines in neutral gray. Line numbers display on both sides for precise reference. Scroll through the comparison to review all changes. The diff calculation happens entirely in your browser using JavaScript string analysis algorithms.

Developers compare code file versions to review changes before committing to version control systems. Writers track revisions between draft versions to see what was added, removed, or modified during editing. Translators compare source text with translated versions to verify all content was accurately converted. Contract reviewers highlight differences between agreement versions to identify altered terms or clauses. Students check their revised essays against earlier drafts to confirm all instructor feedback was addressed.

Format both texts consistently before comparing to avoid false positives from spacing or line break differences. Use line-by-line comparison for code or structured text, but consider word-level diff tools for prose. Save diff results as screenshots or copy-paste into documentation when you need to archive comparison results. For code, integrate proper version control like Git instead of manual diff checking for production workflows. Normalize whitespace, line endings, and character encoding before comparing technical files to eliminate noise from the diff output.

All processing happens directly in your browser. Your files never leave your device — no server uploads, no cloud storage, no data retention. The tool works offline once loaded, requires no registration, and is completely free with no usage limits.