Text Diff Checker

What this tool does

This tool compares two blocks of text line by line and shows a unified diff: lines only in the original are marked as removed, lines only in the changed version are marked as added, and matching lines are shown unchanged. It uses a longest-common-subsequence algorithm — the same underlying approach as command-line diff and Git's diff view — computed entirely in your browser.

Example use case

Comparing two versions of a config file, a paragraph of copy that went through an edit pass, or a chunk of code pasted from two different branches all benefit from a line-level diff instead of reading both blocks side by side and spotting differences by eye, which is slow and error-prone for anything longer than a few lines.

Note on large inputs

Computing an exact diff is quadratic in the number of lines on each side, so extremely large documents (thousands of lines) may be slow or get rejected with a message asking you to compare a shorter excerpt instead.