What happens when you accept an AI edit without actually reading it? That single habit explains most of the mysterious bugs developers blame on Cursor. The tool isn’t usually wrong about what you asked. It’s wrong about everything you didn’t ask it to touch. That’s why the choice between a diff review and a rewrite-and-accept flow is the most consequential setting in your day.
This piece breaks down how those two workflows differ in practice, where each one earns its keep, and the mistakes that turn a helpful agent into a codebase-wide liability.
What the diff and rewrite modes actually do
Every AI code tool has to answer one question: how much of your file does the model get to replace? The answer determines how much you can review.
A diff-based flow shows you a line-level comparison between your current code and the proposed code. You see exactly which lines were added, removed, or modified, and you can accept or reject them in chunks. Nothing outside the changed lines moves.
A rewrite flow replaces a whole file, function, or block with a freshly generated version. The model regenerates everything, including lines that had nothing to do with your request. You review the output as a finished product rather than as a set of changes. (Git Basics: recording changes and reviewing diffs)
The distinction sounds cosmetic. It isn’t. In a diff, an unrelated function that got quietly altered shows up as a visible deletion. In a rewrite, it just… isn’t there anymore, and you have to notice its absence.
Why the diff view is the safer default for large codebases
Picture a 900-line service file with authentication logic, database calls, and error handling. You ask the agent to add rate limiting. In a rewrite flow, the model regenerates the entire file. Even if it gets rate limiting right, it may also “improve” your error messages, drop a defensive null check, or reformat your imports.
None of that shows up as a decision you made. It shows up as a file you accepted.
Diff review forces those changes into the open. You see the rate-limiting block added, and you also see the null check removed three hundred lines down. That visibility is the whole point. The underlying concept is the same one version control has relied on for decades: a diff is a description of change, and change you can’t describe is change you can’t trust.
This is the same principle behind the problems covered in our breakdown of how Cursor lint and AI edits auto-rewrites cause damage, where small automatic rewrites compound into real breakage.
When rewrite mode is genuinely better
Rewrite flows aren’t a mistake. They’re a tool with a narrow but real use case.
If 80 percent of a file is changing anyway, a line-by-line diff becomes noise. You’d spend more time reading red and green than you’d spend writing the code yourself. Greenfield files, aggressive refactors, and files you’re replacing wholesale are all reasonable rewrite candidates.
The rule of thumb that works in practice: rewrite when you expect most lines to change, diff when you expect a few. If you can’t predict which, default to diff. The cost of an extra review is minutes. The cost of a missed regression is a debugging session that eats an afternoon.
A practical comparison of the two workflows
| Dimension | Diff review | Full rewrite |
|---|---|---|
| What you see | Only changed lines | Entire regenerated file or block |
| Unrelated code | Preserved unless explicitly touched | Regenerated, may drift |
| Review speed on small edits | Fast | Slow, requires full re-read |
| Review speed on near-total rewrites | Slow, noisy | Fast |
| Risk of silent regressions | Low | Moderate to high |
| Best for | Focused changes in existing files | New files, heavy refactors |
| Rollback granularity | Per hunk | Per file |
The table makes the tradeoff obvious, but the real lesson is about review attention. Humans are bad at reading long outputs carefully. A 40-line diff gets read. A 900-line rewrite gets skimmed, and skimming is where bugs slip through.
Common mistakes that make both workflows fail
Accepting without reading the whole diff
The most frequent failure isn’t picking the wrong mode. It’s picking the right mode and then not looking. A diff only protects you if you scroll it. Agents often make small changes far from the cursor position, and those are exactly the ones people miss.
Letting the agent touch files you didn’t mention
Multi-file agents will happily edit a utility module to make their change compile. That’s sometimes correct and sometimes catastrophic. Before accepting, check the file list. If a file appears that you never discussed, read its diff first. (Diff (Wikipedia): how file comparison algorithms work)
Using rewrite mode on files with uncommitted work
If a rewrite goes wrong and you haven’t committed, you’re reconstructing from memory. Commit before any large agent operation. This one habit prevents more lost work than any setting.
Treating the diff as proof of correctness
A clean diff shows what changed. It says nothing about whether the change is right. Tests still matter. The diff tells you where to look, not whether to stop looking.
There’s a useful parallel in how other AI editing tools handle scope. Our comparison of Cursor patch versus rewrite and what AI edits actually change in your code digs into why patch-style edits preserve context that full rewrites discard.
How the underlying edit model shapes what you can review
Diff and rewrite aren’t just UI choices. They reflect different edit strategies underneath.
A patch-based strategy asks the model to produce a minimal set of changes against a known baseline. The model must specify context lines and target locations. That constraint makes unintended edits harder, because every change has to be anchored to something.
A generative rewrite strategy asks the model to produce a complete artifact. It has more freedom, which is both the strength and the danger. Freedom to restructure is freedom to drift.
This matters more as codebases age. A file written last month is easy to regenerate faithfully. A file with five years of accumulated special cases, workarounds, and comments explaining why a weird check exists is not. Models don’t know why that check is there. They only know it looks redundant.
That’s the strongest argument for diff-first workflows in mature codebases: they preserve institutional knowledge the model can’t see.
Where agentic behavior changes the calculus
Modern coding agents don’t just edit one file. They read, plan, run commands, and iterate. That autonomy raises the stakes on how changes land.
When an agent makes twenty edits across eight files, a rewrite flow gives you twenty regenerated artifacts to inspect. A diff flow gives you twenty small, reviewable changes with visible boundaries. The diff wins almost every time, because review effort scales with the size of what you’re reading, not the number of edits.
The broader shift toward agents that act rather than suggest is covered in our piece on agentic AI versus generative AI and the key differences, which explains why autonomous tools need tighter review loops, not looser ones.
Practical tip: when an agent proposes a multi-file change, review the smallest diffs first. They’re quick, and they often reveal the agent’s assumptions before you reach the big one.
Building a workflow that holds up
A durable workflow doesn’t depend on which mode is fashionable. It depends on a few habits layered on top of whichever mode you pick.
- Commit before every agent session, so any outcome is recoverable.
- Read the file list before reading any diff.
- Review the smallest changes first to catch wrong assumptions early.
- Run tests after accepting, not before.
- Keep a scratch branch for experimental rewrites so they never touch your working branch.
These steps cost almost nothing and catch the failures that matter. They also make you faster over time, because you stop re-reading code you already verified.
One more habit worth building: keep a short note of what you asked the agent to do. When you review the diff twenty minutes later, that note is your specification. Without it, you’re judging the change against a vague memory of your own request, and vague memories approve bad code.
What to expect as the tooling evolves
The trend line is clear even without a roadmap. Editors are converging on reviewable, incremental changes because that’s what developers actually trust. Full-file regeneration is becoming a fallback for cases where incremental editing is impractical, not the default.
That means the skill worth developing now isn’t memorizing a particular mode’s behavior. It’s getting fast at reading diffs. Developers who can scan a 60-line change and spot the one wrong line will outperform developers who can generate code quickly but review it slowly, regardless of which tool they use.
The same pattern shows up across AI-assisted work generally. Speed of generation is rarely the bottleneck. Speed and quality of verification is. Every tool that gets good at producing output eventually has to get good at showing you what it did.
Conclusion
The choice between diff review and full rewrite comes down to one question: how much of this change do you actually need to see? For focused edits in existing files, the diff is safer, faster to review, and far less likely to quietly delete something you needed. For wholesale replacements, a rewrite saves you from reading noise.
What matters more than the mode is the discipline around it. Commit first. Read the file list. Review the small changes before the big ones. Run the tests. These habits turn an unpredictable agent into a predictable one, and they’ll keep working long after the interface changes again.
If you take one thing away, take this: the diff is a conversation about your code, and the rewrite is a replacement for it. Choose the conversation unless you genuinely want the replacement.
FAQ
What is the difference between diff and rewrite in Cursor Composer?
A diff shows only the lines that changed, so you can review and accept them in pieces. A rewrite replaces an entire file or block with newly generated code. The diff preserves everything you didn’t ask to change. The rewrite regenerates it all, which means unrelated code can shift without you noticing.
Which mode should I use for a small change in a large file?
Use the diff. A small change in a large file is exactly the case where rewrite mode is most dangerous, because regenerating hundreds of lines to add ten creates hundreds of opportunities for silent drift. The diff keeps the blast radius equal to the size of your request.
Is rewrite mode ever the right choice?
Yes, when most of the file is changing anyway. Greenfield files, heavy refactors, and wholesale replacements are all reasonable rewrite candidates. If reading the diff would take longer than reading the new file, the rewrite is the more efficient path.
Why do AI edits sometimes change code I never mentioned?
Agents often adjust supporting code to make their change compile or to satisfy a linter. Sometimes that’s correct. Sometimes it breaks an assumption the model couldn’t see. Checking the file list and reading small diffs first is the fastest way to catch these before they spread.
Does a clean diff mean the code is correct?
No. A diff tells you what changed, not whether the change is right. It’s a map of where to look, not a guarantee. Tests, type checks, and a quick read of the surrounding logic still do the actual verification work.
How do I make agent edits safer without slowing down?
Commit before every session, review the file list before any diff, and read the smallest changes first. Keep experimental rewrites on a scratch branch. None of these add meaningful time, and together they catch the failures that cost hours.
