A diff checker compares two versions of text and highlights exactly what changed between them. It shows lines that were added, removed, or left unchanged — the same way developers review code in Git, GitHub, or similar version control systems.

Common use cases include code review (spotting bugs introduced in a new version), version control (understanding what changed before committing), config changes (comparing old vs. new server configs or JSON files), and contract/document comparison (finding edits between revisions of a contract, essay, or legal document).

This diff checker uses a line-based Longest Common Subsequence (LCS) algorithm — the same approach behind git diff and Unix diff. It runs entirely in your browser; your text never leaves your device.