Diff Checker

Text diffing compares two texts and identifies what's been added, removed, or changed. Under the hood, most diff algorithms use a variant of the Longest Common Subsequence (LCS) problem — finding the longest sequence of lines that appear in both texts in order.

Lines present in only the first text are marked as deletions (red), lines present in only the second text are additions (green), and matching lines are unchanged. This is the same approach used by git diff, GitHub pull requests, and code review tools.

Diff checking is essential for debugging configuration changes, comparing API responses before and after a code change, reviewing document edits, and verifying that a minifier or formatter didn't alter your code's behavior. This tool runs entirely in your browser with zero server interaction.