About Text Diff
Working out what changed between two versions of something is a job people do constantly and badly — reading two documents side by side and hoping to spot the difference. A diff does it exactly, and shows you the answer in seconds.
This compares line by line using a longest-common-subsequence algorithm, the same approach version control systems use. That matters because a naive line-by-line comparison marks everything after an inserted line as changed; an LCS diff correctly identifies the single insertion and leaves the rest alone.
Options let you ignore case and normalise whitespace before comparing, which is what you want when the only real question is whether the content differs rather than the formatting.
How to compare two texts
Paste the original
Put the first version in the left box.
Paste the modified version
Put the second version in the right box.
Choose the view
Unified shows one column with markers; side-by-side shows both.
Read the differences
Added lines are green, removed lines red, and the summary counts each.
Good uses for a diff
- Checking exactly what an editor changed in a draft.
- Comparing two configuration files to find the setting that differs.
- Seeing what changed between two API responses.
- Verifying that a copied block of text is identical to its source.
- Reviewing a contract revision without reading the whole thing again.