How to see what your AI changed in a document

Why not just trust the AI's summary?

You shouldn't just trust an AI's summary of its changes, because a summary is the AI's description of its work, and descriptions leave things out. "Tightened the intro" might also mean a deleted paragraph, a changed number, or a renamed heading three pages down.

A diff shows you the file itself. A diff is a before-and-after view that marks each added and removed line. It takes a minute to read, and it never forgets an edit.

the summary is the trailer. the diff is the film.

Which method should I use to see what an AI changed?

Pick a method for seeing what an AI changed by where the file lives. This table compares eight methods. Most people need only the first row that fits.

How do I use git diff to see what an AI changed?

If the file is in a git repository, git diff shows exactly what the AI changed since your last commit. This is the most reliable check, because git compares the file against the last saved snapshot (a commit).

In Terminal, inside the project folder:

git diff -- plan.md

Lines starting with - were removed. Lines starting with + were added. For prose, where one word changes in a long line, this is easier to read:

git diff --word-diff -- plan.md

It shows removed words as [-like this-] and added words as {+like this+} (git docs).

You don't have to leave your AI tool:

• Claude Code: type /diff to review "the edits Claude has made so far alongside anything else you haven't committed" (Claude Code docs).
• Codex CLI: /diff shows "the Git diff, including files Git isn't tracking yet" (OpenAI docs).

To undo a change rather than read it, Claude Code's /rewind restores files from the checkpoints it keeps of its own edits (Claude Code docs).

Commit before you ask the AI for a big rewrite. Then git diff shows exactly that rewrite and nothing older.

What if the file the AI changed isn't in git?

If the file isn't in git, keep a copy before the AI starts, then compare the two. It sounds old-fashioned, and it works everywhere.

1. Duplicate the file before you ask for changes. In Finder, select it and press ⌘D (Apple Support). In Terminal: cp plan.md plan-before.md
2. Let the AI edit plan.md.
3. Compare the two files with one of these.

In VS Code: right-click plan-before.md in the Explorer and choose Select for Compare. Then right-click plan.md and choose Compare with Selected (VS Code docs). You get the two side by side with changes highlighted.

In VS Code, without a second file: copy the whole file's text before the AI edits it. Afterwards, open the file and run File: Compare Active File with Clipboard from the Command Palette (VS Code docs).

In Terminal: git can compare any two files on disk, even outside a repository (git docs):

git diff --no-index --word-diff plan-before.md plan.md

Does VS Code keep a file history I can compare?

Yes, VS Code keeps a local file history, for saves made in VS Code. Its Timeline view, at the bottom of the Explorer, lists local file history. From an entry you can compare with the current file or restore it (VS Code docs).

The catch: VS Code's docs describe an entry being added each time you save in the editor. If Claude Code or Codex edits the file from a terminal, don't count on Timeline having caught the version before. Use git or a copy for those.

If the AI works inside VS Code, through an extension, check the extension's own change view first. It's usually the quickest.

Can macOS show me an older version of a document?

Sometimes. macOS can show older versions of a document in apps that support it, like TextEdit. Many Mac apps save versions of a document as you work. Open the document and choose File › Revert To › Browse All Versions (Apple Support).

Apple says a version is saved automatically every hour, and also when you open, save, duplicate, lock, rename or revert a document. So if the file was open in a supporting app like TextEdit before the AI changed it, there may be a version from before.

Two limits. It only works in apps that support it, and code editors and most Markdown apps don't. And it shows versions side by side without marking what changed, so you compare by eye.

Should I ask the AI for a list of its changes?

Yes, ask the AI for a list of its changes, but treat it as a map. Then check the map against the file. This prompt gets a useful list:

List every change you made to plan.md.
For each one, quote the old text, then the new text.
Include deletions. Don't summarize.

Quotes let you search the file for each change in seconds. If the AI lists three changes and a diff shows five, you've learned something about the next summary it gives you.

How do I see an AI's changes as they happen?

To see an AI's changes as they happen, use a reader that watches the file. One Clear Reader reloads the page when the AI saves, keeps your place, and tells you what moved. This table shows what each of its change features does and which plan it's in.

The first two are the "I just asked Claude to revise this" workflow. Keep the file open, ask for the change, and jump straight to the new parts instead of rereading the whole thing.

Version history is the safety net. Because it keeps a copy before outside changes too, an AI rewrite you don't like is one Restore away.

For plans specifically, reviewing a Claude Code plan before you approve it uses the same markers to check a revision. If you'll be editing the file yourself afterwards, see how to edit a .md file without breaking it. And if you're weighing this against staying in VS Code, here's One Clear Reader compared with VS Code.

Questions people ask