Text Diff Checker
Compare two blocks of text and highlight additions, deletions, and changes line by line.
How text diffing works
Text diffing compares two documents and identifies the minimal set of changes — insertions, deletions, and unchanged lines — needed to transform one into the other. The algorithm used is the Longest Common Subsequence (LCS), first described by computer scientists in the 1970s.
The Unix diff utility (1974) pioneered the format still used today: lines starting with + are additions, lines starting with − are removals, and unchanged lines provide context. Git uses this format internally to track every change in your codebase.
Diff tools are essential for code review, proofreading edits, comparing API responses, and verifying configuration file changes. This tool performs a line-by-line diff entirely in your browser — no text is sent to any server.