Text Diff Checker

How this calculator works

Reading two long versions of the same document side by side is how small changes slip through: a tweaked number in a contract, a dropped paragraph in an essay, one wrong line in a config file. A diff checker does the tedious comparison for you. Paste the original text in the left box and the revised text in the right, press Compare, and every line that was added shows in green, every line that was removed shows in red, and lines that did not change stay plain. Inside a changed line pair, the exact words that differ are highlighted, so you do not re-read whole lines to find one edited word.

The comparison itself is the same idea behind the Unix diff command from 1974 and the git diff developers use every day: find the longest sequence of lines both versions share, and report everything else as an addition or a removal. This tool runs that comparison entirely in your browser, so contracts, drafts and config files you paste are never uploaded anywhere. Worked example: an original club notice reading "The club meets on Friday at 5 pm." revised to 6 pm, with a new line "Sign-up closes on March 1." inserted, produces exactly one changed pair (5 highlighted in red, 6 in green) and one added line, and the summary reads 1 line added, 1 line removed, 3 unchanged.

Two options hide differences you do not care about. Ignore whitespace treats lines as equal when they differ only in indentation or trailing spaces, which is what you want after reformatting code or copying text between tools that use tabs versus spaces. Ignore case treats London and LONDON as the same line, useful for comparing SQL or config keys that were uppercased. Turn on Only show changes to collapse long unchanged stretches and jump straight to the edits. The Copy diff button gives you a unified diff (removed lines marked -, added lines +) you can paste into a review or ticket, and Download .patch saves the same output as a file.