Committing Without Knowing What AI Changed? Check with /diff

You told Claude "fix this" and a bunch of files changed in a cascade. But did you see exactly what changed and how? Committing (saving) without looking, then having an incident later from one unintended line — you experience this now and then while vibe coding. /diff prevents this. It's a final pre-commit check tool that shows you what changed, in color, at a glance.

Definition

/diff is a command that shows, in color, changes that haven't been saved (committed) yet.

Here, "commit" is the act of confirming changes into a single record and saving them. Before committing, you're in a "changed but not yet confirmed" state, and /diff shows exactly the changes in that state.

On screen it's usually displayed like this.

• Added lines: green (or a + mark)
• Deleted lines: red (or a - mark)

So you can see right away, just from the color, what's newly in and what's been removed. ("diff" is short for difference.)

How to use it (by difficulty)

Basics — view changes

After Claude fixes the code, type into the chat box.

/diff

On entering it, a screen appears with the not-yet-saved changes shown in color. Green is added, red is deleted. It's the step where, before committing, you visually confirm "did it change the way I intended?"

Applied — view by turn

/diff

With the /diff screen up, pressing the left/right arrow keys lets you move between the changes of each step (turn) Claude worked on. Useful for pinpointing changes at a specific moment, like "what did it change in the 3rd step."

Advanced — navigate by file

/diff

If several files changed at once, on the /diff screen you can review them by moving file by file with the up/down arrow keys. When there are many files, you page through them one by one to review without missing anything.

Common pitfall — /diff only "views," it doesn't undo

It's easy to confuse, but /diff only shows the changes. Pressing something here doesn't cancel or revert changes. It's just a "review screen."

So the flow goes like this.

1. Check the changes with /diff.
2. If you find a part that differs from your intent, request again in conversation, "fix this line here like so."
3. Commit when you're satisfied.

Remember that /diff is the "eye that checks," and fixing is still assigned through conversation.

A real case

I once had Claude fix several files at once. Looking only at the result, it seemed fine, but out of habit I turned on /diff. Skimming the step-by-step changes with the left/right arrows, I found that in one file, a perfectly good line had been deleted contrary to my intent.

/diff

I immediately requested "bring back that line you just deleted" and reverted it. Had I committed as-is, it would have been a bug I'd wander around for ages over later. One /diff before committing prevented the accident.

Use it like this too

• Check before saving: Always lay eyes on the changes once before committing.
• Track changes by turn: Check each step's changes separately with the left/right arrows.
• Navigate by file: Review file by file thoroughly with the up/down arrows.
• Pre-code-review check: Before entering a full review, skimming quickly first with /diff is efficient.

Tip: Skipping the look thinking "the AI surely did it well" is vibe coding's most common cause of accidents. Even if a change looks small, make /diff before committing a habit.

How others use it

• Beginners see a noticeable rise in work efficiency just from properly using three: /plan, /diff, /compact. — Frequently Used Slash Commands (Dale Seo)

Wrap-up

The key is one sentence. Before committing, always check what changed with /diff. As much as AI changes a lot fast, the responsibility to review those changes remains with the human. One line of /diff prevents the accident you'd otherwise miss in advance.

Based on: Claude Code v2.1.154 (2026.05)