Text diff checker

How it works

The tool splits both texts into lines, then builds a longest common subsequence table over the two line arrays. The table finds the largest set of lines that appear in both versions in the same order; everything outside that set is a change. Each line of the result carries a prefix: a space for an unchanged line, a minus for a line only the first version has, and a plus for a line only the second version has. Counts for added, removed and unchanged lines appear with the result, so a large change is obvious at a glance. Both inputs are capped at 40,000 characters and 1,000 lines so a huge paste cannot lock the tab, and the result is rendered as plain text rather than HTML so nothing in your text can become markup.

Worked example

Compare a first version with the lines alpha, beta and gamma against a second version with alpha, beta two, gamma and delta. The checker keeps alpha and gamma as unchanged, reports beta as removed, and reports beta two and delta as added: one removed, two added, two unchanged. Comparing a text with itself reports zero changes and says the two versions are identical.

Questions and answers