Reverse a Unified Diff

About this tool

A reverse patch is the text you would apply to undo a change. Paste the output of git diff, git show, git format-patch, diff -u, or a bare unified hunk, and this tool emits the inverse patch: old and new hunk ranges swap, + lines become -, - lines become +, and git metadata is flipped so the result behaves like a revert.

Worked example — given this patch:

diff --git a/src/main.rs b/src/main.rs
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,4 @@
 fn main() {
+    println!("hello");
 }

the default output is:

diff --git a/src/main.rs b/src/main.rs
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,4 +1,3 @@
 fn main() {
-    println!("hello");
 }

Save that output and apply it with your usual patch tool to remove the line. Nothing is applied here; the tool only rewrites the patch text.

Git headers it understands

Real diffs are more than @@ hunks. The reverse operation also handles the metadata that makes a patch apply cleanly:

• index old..new blob hashes swap by default. Choose Drop index lines when the hashes are stale or the target repository may not have the old blobs.
• new file mode becomes deleted file mode, and old mode / new mode pairs swap.
• rename from / rename to and copy from / copy to swap.
• --- / +++ paths and the two sides of diff --git swap when Swap file paths is on, which is the default.
• \ No newline at end of file markers stay attached to the line they describe after the line changes side.

Output modes

• Reverse patch returns the inverted patch text.
• Summary report lists the files, hunk counts, swapped plus/minus totals, and each reversed hunk header next to the original one.
• JSON report + patch returns the same report as structured data with the reverse patch under patch.

Use File filter for a multi-file patch: full path, suffix on a directory boundary, or bare filename all match. Leave it blank to reverse every file section.

Limits and edge cases

• Input is capped at 1 MB.
• Binary patches cannot be inverted from the forward delta alone. The default is to fail and name the binary file; Skip drops those sections, and Keep passes them through unchanged with a warning.
• Combined merge diffs with @@@ headers are rejected. Diff against a single parent first.
• This tool does not apply patches, search your working tree, resolve conflicts, or do fuzzy matching. Use an apply-patch tool for reverse-apply and conflict handling.
• CRLF line endings, final-newline state, mail-style preambles, and bare @@ hunks are preserved where possible.

FAQ