μdiff

A coding agent writes faster than you can read and hands you everything at once. μdiff turns that pile into a review: it shows the edits in batches as they land, remembers what you have already signed off, and lets you write comments and replacements against the lines themselves.

• Anything that produces a unified diff. μdiff reads it on standard input, so git diff, gh pr diff, diff -u on two loose files, or a patch from a mailing list all work the same. No repository required.
• One binary, about 3 MB, with no runtime beside it.
• The review leaves as plain text. One key copies it in GitHub's suggestion syntax — paste it into your agent, into a pull request, into a message. No plugin, no protocol, no session to keep open.

Point μdiff at the directory the agent is editing and leave it open:

udiff --watch .

Each time the agent pauses, its edits arrive as a new revision. { and } move between revisions, Space marks a file you are happy with, c selects lines you are not, and Shift+Y copies every note you left — across every revision, skipping the files you marked reviewed.

Paste that into the agent and it has your review in a form it can act on. Nothing is written to disk and no repository is required, so it works on a scratch directory as well as on a checkout.

An hour of work is hard to remember in full. Read it before it becomes a commit:

git diff | udiff
git diff --staged | udiff

This is where the forgotten dbg!, the half-finished branch, and the file you never meant to touch turn up.

git diff main..HEAD | udiff
gh pr diff 42 | udiff
cat changes.patch | udiff

Press r on a line to write a replacement instead of a comment. Suggestions come out in GitHub's own review syntax, so a review you pull down with gh goes back up as a pull request comment unchanged.

Useful for generated output, configuration that has drifted, or a before and after:

diff -u old.rs new.rs | udiff
diff -ru old-dir/ new-dir/ | udiff

Git can do the same for files outside a repository:

git diff --no-index --no-color -- old.rs new.rs | udiff

Notes attach to the lines they belong to — a comment, or a replacement you write yourself:

Shift+Y copies them as plain text. A comment:

1. src/main.rs (old lines 3; new lines 3-4)
Selected diff:
-old
+new
Comment: this allocation is redundant

A suggested replacement, in GitHub's syntax:

2. src/main.rs (new lines 12)
Selected diff:
+    let value = compute().unwrap();
Suggested replacement:
```suggestion
    let value = compute()?;
```

Comments live only for the current run. μdiff produces a review; it does not store one.

brew install aliev/tap/udiff

macOS and Linux:

curl --proto '=https' --tlsv1.2 -LsSf \
  https://github.com/aliev/udiff/releases/latest/download/udiff-installer.sh | sh

Windows PowerShell:

powershell -ExecutionPolicy Bypass -c "irm https://github.com/aliev/udiff/releases/latest/download/udiff-installer.ps1 | iex"

From source:

cargo install --path udiff --locked

Press ? for the full list. p finds a file by name, j/k and the arrows move, s shows the diff side by side, b brings up the file list, Tab switches to it, q quits.

Copying uses OSC 52, so the terminal has to allow clipboard access from programs.

μdiff asks the terminal what colour its background is and follows the answer. Set UDIFF_THEME=light, dark or mono to decide for it — inside tmux or screen, where the question cannot be asked, you will have to. NO_COLOR is honoured and outranks both.

Feed μdiff an uncolored diff. Tools like delta emit terminal styling meant for human eyes, which μdiff cannot parse — pipe it the original git diff instead.

diff and git diff --no-index exit with status 1 when they find differences. A shell running with pipefail will report the whole pipeline as failed.

Start with ARCHITECTURE.md, then CONTRIBUTING.md. Release notes live in CHANGELOG.md. μdiff is available under the MIT License.