Free Diff Checker Online

The Diff Checker is a free online tool that compares two pieces of text or code and highlights differences line by line for easy review.

Yes, it is completely free with no registration required. All comparison happens client-side in your browser.

No, all comparison happens locally in your browser. Your code and text are never sent to any server.

Yes, the Diff Checker is fully responsive and works on smartphones and tablets. You can use it on any device with a modern web browser -- no app download required.

No account or registration is needed. Simply open the Diff Checker in your browser and start using it immediately. There are no sign-up walls or usage restrictions.

Simply enter your input in the provided field, adjust any settings to your preference, and the tool will process it instantly. You can then copy the result to your clipboard or download it.

The Diff Checker works in all modern browsers including Chrome, Firefox, Safari, Edge, and Opera. For the best experience, use the latest version of your preferred browser.

These three modes control how finely the tool splits your text before comparing it. Line mode, the default, treats each whole line as a single unit and is ideal for source code and structured data where a line is a meaningful block. Word mode breaks text on spaces, so a sentence that changes only a few words is flagged word by word instead of marking the entire line as changed, which is perfect for prose and editing drafts. Character mode is the most precise level, comparing one character at a time to catch a single typo, a flipped digit, or a stray space. The same Longest Common Subsequence logic runs underneath each mode; only the unit of comparison changes. Pick the granularity that matches your content above and the highlighting adjusts instantly.

A unified diff is a standard, compact way of describing changes in a single column: each line is prefixed with a space for unchanged content, a minus for removed lines, and a plus for added lines, under a header that names both files and the line ranges. Because Git, GitHub, and most version-control tools read this exact format, it travels well between people and systems. The patch export here produces the same content as a .patch file, which is what you hand to commands like git apply or patch to replay an edit on another copy of the file. Use unified output when you just want a readable, shareable record of what changed, and patch when someone needs to actually apply those changes elsewhere. Choose either from the export menu after comparing your two versions above.

The similarity percentage is a quick read on how alike your two versions are, derived from the comparison the tool already computed. After aligning both texts, it counts how many units stayed unchanged versus the total number of units across the result, then expresses the unchanged share as a percentage. Two identical files score 100 percent, while files that share almost nothing approach zero. Because the count depends on the granularity you picked, the same pair can read differently in line mode versus word or character mode, since each splits the text into different units. It is a relative drift indicator rather than a formal plagiarism score, but it is genuinely useful for spotting near-duplicate files or confirming an edit was small. Paste both versions above and the percentage appears in the stats summary alongside the add and remove counts.

You have two ways to load files without copying and pasting. Click the upload control on either the Original or Modified panel and pick a file, or simply drag a file from your desktop and drop it directly onto the panel you want to fill. The tool reads the file's text on your own device and uses its name as the panel label, so the comparison stays clearly identified. Common text and code formats are accepted, including .json, .js, .ts, .py, .html, .css, .md, and .yml among many others. Nothing is uploaded to a server, which makes it safe to compare a private config file or unreleased source code. Once both sides are loaded, a swap button lets you flip them if you got the order backwards. Drop your two files above to see the differences instantly.

The ignore options only suppress the specific kinds of noise you enable, so anything outside those categories still shows up as a real change. You can disregard case differences, collapse runs of whitespace, strip trailing spaces, drop blank lines, or remove comments, and each toggle is independent, meaning a difference you still see simply was not covered by the boxes you checked. For example, ignoring whitespace will not hide a renamed variable, and ignoring comments will not mask a changed value inside actual code. The ignore step also runs before the comparison, so it affects which lines are matched, not just how they are colored. If unexpected changes persist, switch to word or character mode to see exactly which characters differ. Enable the relevant ignore options above to focus only on the edits that matter to you.