Diff Checker

Compare two texts line by line with added/removed highlighting. Free, runs entirely in your browser — no signup, and nothing you paste in is uploaded.

A line diff is built on the longest common subsequence — the longest ordered set of lines present in both texts, with everything else classed as an insertion or a deletion. That framing explains the behaviour that surprises people: move a paragraph and the diff shows it deleted in one place and added in another, because order is part of what is being compared.

Line granularity is a deliberate trade. It reads well for code and configuration, where a line is roughly a unit of meaning, and badly for prose that has been reflowed, where changing one word can mark an entire paragraph as rewritten.

The comparison worth running more often than people do is the same config from two environments. Drift between staging and production is rarely a dramatic difference; it is one flag, one timeout, one URL, sitting in a file nobody has read end to end in months.