Free Online Diff Checker
Compare two texts or code snippets and see exactly what changed — line-by-line diff with color highlighting, free and 100% client-side.
100% Client-Side · Your data never leaves your browserHow to Use Diff Checker
Paste your Original text on the left and the Modified version on the right. Click Compare (or press Ctrl/Cmd+Enter) to compute the diff.
The output shows:
- Green lines (+) — lines added in the modified version
- Red lines (−) — lines removed from the original
- Unmarked lines — lines that are identical in both versions
Line numbers on the left column refer to the original, and the right column refers to the modified version. A summary above the diff shows the total count of added, removed, and unchanged lines.
Frequently Asked Questions
What algorithm does this diff tool use?
It uses a Longest Common Subsequence (LCS) algorithm — the same underlying approach as the Unix diff command. It computes the minimal set of line additions and deletions needed to transform the original text into the modified text.
What do the + and − symbols mean?
Lines marked with + (green) are present in the modified text but not in the original — they were added. Lines marked with − (red) are in the original but not in the modified — they were removed. Unmarked lines are identical in both.
Can I compare code files?
Yes. Paste the contents of any text-based file — source code, configuration files, JSON, Markdown, SQL scripts, etc. The comparison is purely text-based, so any file format that can be opened in a text editor works.
Is there a size limit?
The tool caps each side at 400 lines to maintain instant performance in the browser. For larger files, consider using git diff or a desktop diff tool like VS Code's built-in diff editor.
Does this tool do word-level or character-level diffing?
Currently the diff is line-level: each line is compared as a whole unit. This is the most readable format for code and prose. Word-level highlighting within changed lines may be added in a future update.