A diff (short for 'difference') compares two pieces of text line by line and shows what changed: additions (lines only in the modified text), deletions (lines only in the original), and unchanged lines. This tool uses a longest-common-subsequence (LCS) algorithm to produce an accurate comparison instantly in your browser.

Yes. Paste any plain text into either pane — source code, configuration files, JSON, Markdown, or prose. The tool does a line-by-line diff, so it works best when content is structured by newlines.

No. The comparison runs entirely in your browser. Your text is never uploaded or stored anywhere.

Cyan lines (marked with +) are additions that appear in the modified text but not the original. Red lines (marked with -) are deletions present in the original but removed in the modified version. Unchanged lines are shown without color.

There is no hard limit imposed by the tool. Very large texts (hundreds of thousands of lines) may make the browser slow while computing the diff, but smaller documents compare instantly.