Diff Checker

"What changed between these two versions?" is one of the oldest questions in working with text, and eyeballing two documents side by side is the least reliable way to answer it. A diff checker answers it mechanically: paste the original on the left, the new version on the right, click Compare, and every difference is highlighted — removed lines in red with a − sign, added lines in green with a +, unchanged lines left plain for context.

Under the hood this uses a longest-common-subsequence algorithm — the same family that powers git diff — which is why the output feels familiar if you've ever reviewed a pull request. A changed line appears as its old version removed and its new version added, adjacent, so the edit reads naturally. The summary line counts additions and removals at a glance, and explicitly tells you when the two texts are identical — sometimes the most useful answer of all, instantly settling "did anything actually change?"

Practical uses are everywhere: comparing contract revisions a client sent back, checking what a colleague edited in your copy, verifying two config files match across environments, or spotting the one-line difference between working and broken code. Both texts stay in your browser — safe for contracts, credentials-adjacent configs and anything else you'd rather not upload to compare.