What is a unified diff?

A unified diff is the standard patch format used by git and the patch tool. It shows changed regions as hunks with an @@ -l,s +l,s @@ header, prefixing removed lines with minus, added lines with plus, and unchanged context lines with a space.

How are the changes computed?

The tool runs a longest-common-subsequence diff over the lines of both inputs to find the minimal set of insertions and deletions, then groups them into hunks and pads each hunk with your chosen number of context lines.

What do the context lines do?

Context lines are the unchanged lines printed around each change so the patch can be located reliably even if surrounding code shifts. Three lines is the git default; increase it for fragile files, decrease it for a terser patch.

Can I apply the output with git?

Yes. The output uses git-compatible --- a/file and +++ b/file headers and standard @@ hunk markers, so git apply patch-file or patch -p1 < patch-file will apply it, assuming the original matches.

No. Both inputs are diffed entirely in your browser with JavaScript. Nothing is sent to a server, so you can safely diff private or proprietary text.

Unified Diff to Patch File Generator

Q: Is my text uploaded?

No. Both inputs are diffed entirely in your browser with JavaScript. Nothing is sent to a server, so you can safely diff private or proprietary text.

A unified diff is the patch format git and the patch tool understand: it records exactly which lines were removed and added, wrapped in hunks with location headers and a few lines of surrounding context. This generator diffs two pasted texts and emits a clean .patch file you can share or apply offline.

How it works

Both inputs are split into lines.
A longest-common-subsequence (LCS) diff finds the minimal edit script — the smallest set of line deletions (-) and insertions (+) that turns the original into the modified text; matching lines become context ( ).
Consecutive changes are grouped into hunks, each padded with up to N lines of context (default 3) and separated when the gap between changes exceeds 2×N.
Each hunk gets an @@ -start,len +start,len @@ header, and the file gets --- a/<name> / +++ b/<name> headers.

Example

For an original ending color: red; changed to color: blue;, a 1-line-context hunk looks like:

@@ -1,3 +1,3 @@
 .btn {
-  color: red;
+  color: blue;
 }

Notes

Line numbers in the hunk header are 1-based, and the lengths count the context plus changed lines on each side — exactly what git emits. A trailing-newline difference is handled so the patch applies cleanly. Everything is computed locally; your text never leaves the browser.