How to compare two pieces of text line-by-line

1. Paste both versions

   Drop the old version into "Left" and the new into "Right". The tool compares line by line — within-line word-level differences are NOT highlighted; that's a different (and more expensive) algorithm.

2. Press Run

   Result returns an array of `diff` entries with `op` (`equal`, `added`, `removed`) and `text`. The order reflects the merged sequence — equals first, then any insertion/deletion runs, in source order.

3. Reading the output

   Lines marked `added` exist only in Right, `removed` only in Left. Editor UIs typically render added in green and removed in red; the data structure is the same. Trailing newline differences may show up as a single `added`/`removed` line.

4. When line-level is too coarse

   Long unchanged paragraphs with a single word edited will look as one removed + one added pair, not as a word-level diff. For prose review use a dedicated word-diff or character-diff library; line-diff is best for code.