Paste the original and the changed version — added and removed lines are highlighted below.
How it works
The comparison is a classic line-based LCS (longest common subsequence) diff: it builds a dynamic-programming table of the longest run of matching lines between the two texts, then walks it to decide, line by line, whether each one is unchanged, removed, or added — it compares whole lines, not individual words or characters.
FAQ
Does it highlight the specific word that changed within a line, or just the whole line?
Just the whole line — because the diff works line by line, changing a single word in a sentence shows up as one full line removed and one full line added, not a highlighted word inside an otherwise-unchanged line.
Why might it slow down on very large documents?
The LCS algorithm builds a table sized by the number of lines in one text times the number in the other, so its work grows with that product — fine for normal-sized documents, but noticeably slower on inputs with many thousands of lines.
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