What is refactoring?
The alternative to starting again. Here is what it means, and how to choose between fixing and rebuilding.
In short
Refactoring is restructuring the internal design of existing code without changing what it does for the user, done in small steps that each keep the software working and easier to change. It is how technical debt is paid down, and it depends on automated tests to prove that behavior stayed the same.
Also called: Code refactoring, Refactor
Why refactor an AI-built app instead of rebuilding it?
When an AI-built app starts to creak, the tempting answer is to rebuild it. Usually that throws away the most valuable part, the product decisions baked into the screens and flows, and resets the clock on everything that already works. Refactoring keeps what works and changes the structure underneath, one tested step at a time.
If your AI-built app is already breaking for users, our vibe coding rescue works this way: a review of what exists, then tested fixes under the screens you keep.
Refactor or rewrite?
Refactor when the product works, people use it, the problems are local to some parts, and you need to keep shipping meanwhile. Rewrite when the code cannot be tested at all in its current shape, the data model is wrong everywhere, or the platform it runs on is being abandoned.
| Refactor when | Rewrite when |
|---|---|
| The product works and people use it | The code cannot be tested at all in its current shape |
| Problems are local to some parts | The data model itself is wrong everywhere |
| You need to keep shipping meanwhile | The platform it runs on is being abandoned |
How do you refactor code without breaking it?
Make one small change, check that everything still works, and repeat. Martin Fowler describes refactoring as a series of small behavior-preserving transformations, each too small to go far wrong, with the system kept fully working after each one. Tests are the safety net that proves nothing changed for the user.
- 01Cover the behavior firstWrite regression tests around the part you will change, so a broken step shows up at once.
- 02Change one thingRename, extract a function, or merge two copies of the same logic. Run the tests.
- 03Commit and repeatEach passing step is a safe place to stop, so the app can keep shipping between steps.
- 04Keep features separateNever mix a behavior change into a refactoring step. Do the feature as its own change.
What is preparatory refactoring?
Preparatory refactoring means reshaping code just before adding a feature, so the feature fits in cleanly. Fowler sums it up with Kent Beck's line: make the change easy, then make the easy change. It aims cleanup at the code you are about to touch, rather than at a separate cleanup project.
In a Lovable app, this often means merging the several versions of one function that different prompts produced before adding the next feature on top. It is the main way technical debt gets paid down. Before deciding between this and a rebuild, a production readiness check shows where the risk sits.
Common questions
Does refactoring add features?
No. By definition the behavior stays the same. It makes the next feature cheaper and safer to build. When a change needs both, do them as two steps: refactor first with every test still passing, then add the feature on top.
What is the difference between refactoring and rewriting?
Refactoring changes the structure of existing code in small steps while it keeps working, so you can ship throughout. A rewrite throws the code away and builds it again, and nothing ships until it is done. Refactor when the product works; rewrite when it cannot be tested.
Do you need tests before refactoring?
You need some way to prove behavior did not change, and automated tests are the usual one. Fowler notes that without tool support he relies on small steps and frequent testing to catch mistakes. With no tests, write a few around the part you will change first.
When should you refactor?
As part of everyday work, not as a separate project. Fowler often refactors just before adding a feature, so the feature is easy to add, and again afterwards for clarity. Focus on the code you change most often, because that is where messy structure costs you time on every change.
Go deeper
Refactor or rebuild your AI-built app?Refactor or rebuild an AI-built app? A six-area scorecard, the signs a rebuild is right, and how to replace an app piece by piece without stopping it.
Related terms
Read next
Sources
- Martin Fowler: refactoring.com
- Martin Fowler: Definition Of Refactoring (September 1, 2004)
- Martin Fowler: An example of preparatory refactoring (January 5, 2015)
Sources checked October 24, 2026
More on this: Production architecture & security · All glossary terms
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