Refactoring AI-Generated Code: Cleaning Up Without Breaking Things

Your AI-built app works, but the code has become hard to change. One file is 1,200 lines. There are three functions that format dates. Every new feature takes longer and breaks something. The answer usually isn't a rewrite — it's refactoring.

What refactoring is

Refactoring means changing the structure of code without changing its behaviour. The app does exactly the same thing afterwards; the code is just easier to understand and change.

Examples:

Splitting a giant file into smaller ones.
Merging duplicate functions into one.
Renaming things so the names say what they do.
Removing code nothing uses.
Moving logic out of the interface and into a shared place.

The rule that makes it safe: behaviour doesn't change. Refactoring and adding features are separate jobs, done separately.

When to refactor

Good times:

Before adding a feature to a messy area — tidy first, then build.
When the same bug keeps appearing in slightly different places (a sign of duplication).
When your AI tool keeps getting confused by a part of the code.
When you're scared to touch a file.

Bad times:

In the middle of an emergency fix.
On code that works and rarely changes — leave it alone.
Without any way to check you didn't break it (see below).

(Technical Debt in AI-Built Apps explains how the mess builds up in the first place.)

Do it safely

1. Get a safety net

You need a way to tell whether behaviour changed. That means tests for the areas you'll refactor — even a few that cover the main flows. If there are none, the first step is to write them against the current code:

Write tests for the checkout flow as it works today — cart totals, discounts, and taxes — without changing any application code. Run them and make sure they pass.

(How to Write Tests With AI.) Also do a manual click-through of the key flows, and note what you see.

2. Commit a clean starting point

Commit everything before you begin, and work on a branch, so you can always return to a working state. (Git Branches Explained.)

3. Small steps, test after each

One refactoring at a time: split one file, run the tests, commit. Merge one set of duplicates, run the tests, commit. If something breaks, you know exactly which step did it.

4. Review the diffs

A refactoring diff should show code moving and reshaping, not new behaviour. If you see new features, changed logic, or deleted checks, question them. (How to Read a Diff.)

The most valuable clean-ups

Split giant files

Huge components and modules are hard for humans and expensive for AI tools to work with — every edit means reading the whole thing. Split by responsibility: a page into its sections, a big module into focused ones.

Merge duplicates

AI tools often solve the same problem several times. Find the duplicates, keep the best version, point everything at it, delete the rest.

Delete dead code

Unused files, functions, components, and dependencies. They mislead everyone who reads the code — including your AI tool, which may copy an abandoned pattern. Tools like knip can find unused files, exports, and dependencies in JavaScript projects.

Make patterns consistent

One way to fetch data, one way to handle forms, one way to show errors. Pick the best existing pattern and move the others to it — one area at a time.

Name things clearly

handleData2, utils2.ts, and newNewButton tell you nothing. Good names are cheap documentation.

Prompts that keep AI refactoring under control

AI tools can over-reach: asked to tidy one function, they rewrite the module. Be explicit:

Refactor src/components/Dashboard.tsx into smaller components. Do not change any behaviour, styling, or text. Keep all existing props and exports working. Make the change in small steps and run the tests after each.

List every function in the project that formats dates or currency, with file paths. Don't change anything yet.

Find files, components, exports, and dependencies that nothing uses. List them for my review before deleting anything.

Asking for a list first is a powerful habit: you review the plan, then approve the changes. Plan mode does this for larger refactors. (Claude Code Plan Mode.)

Then lock in the result: add the conventions you settled on to CLAUDE.md, so new code follows them. (How to Write a CLAUDE.md.)

Why not just rewrite it?

It's tempting — especially when an AI tool could regenerate the whole app in an afternoon. But the existing code contains every bug fix and edge case discovered so far, most of them undocumented. A rewrite throws those away and rediscovers them one user complaint at a time. Refactor the parts that hurt; rewrite only small, well-understood pieces.

EasySpawn gives Claude Code a persistent workspace with your tests, Git history, and running app in one place — so every refactoring step can be verified before the next one begins. See how it works or join the waitlist.