Untangling the Mess: How to Use Claude Code to Refactor & Clean Up Your Codebase
Hey there, fellow developers. Let's be honest for a second. We've all been there. You inherit a project, or maybe you're just looking back at your own code from six months ago, & you're met with a tangled mess. A spaghetti western of functions, a labyrinth of nested conditionals, & a codebase that makes you want to just
& start over. Technical debt is a real & often painful part of our jobs. But what if I told you there's a powerful new ally in the fight against messy code? Enter Claude Code.
You've probably heard about AI coding assistants, but Claude Code, from Anthropic, is a different beast altogether. It's not just a fancy autocomplete. It's an "agentic" coding tool that lives right in your terminal. This means it can do more than just suggest snippets; it can read your entire codebase, edit files, run tests, & even manage your Git workflow, all through natural language commands. It’s designed to be a collaborative partner, which is a game-changer for something as complex as refactoring.
I've been digging into how to best leverage this tool, & honestly, it's pretty impressive. It's not a magic wand that instantly fixes all your problems, but it's an INSANELY powerful tool that can take on the grunt work of refactoring, freeing you up to focus on the bigger picture. So, let's dive into how you can use Claude Code to bring some sanity back to your projects.
Getting Started: Prepping Your Project for a Claude-Assisted Refactor
Before you let an AI loose on your code, there are a few things you should do to set yourself up for success. Think of it as preparing the operating room before a major surgery.
First things first, you'll need to get Claude Code set up in your local development environment. This usually involves getting an API key from Anthropic & running a simple setup command in your terminal. Once that's done, you're ready to introduce Claude to your project.
A key best practice that came up again & again in my research is creating a
file in the root of your project. This is a markdown file where you can give Claude specific instructions & context about your codebase. Think of it as a style guide or a set of ground rules for your AI partner. For example, you can specify your preferred formatting, naming conventions, or architectural patterns. One developer I read about even fed it rules on how they wanted their SQL queries formatted, & Claude learned to follow them. This simple step can save you a ton of back-&-forth later on.
It's also a good idea to make sure your project is under version control. You'll want to create a new branch before you start any major refactoring. This gives you a safety net to fall back on if things go sideways.
The Refactoring Dance: A Step-by-Step Guide with Claude Code
Okay, so you're all set up. Now for the fun part. How do you actually use Claude to refactor your code? Here’s a general workflow that seems to work well, based on what I've learned from others who have gone through this process.
Step 1: Start with Understanding (Let Claude Do the Reading)
If you're working with a new or particularly complex codebase, your first step is to just understand what you're looking at. This is where Claude's ability to read your entire project comes in handy. You can literally ask it to explain a specific file or function.
One developer, Jacques Bélissent, shared a great example of this. He was faced with a 210-line Python function with a cyclomatic complexity of 16. Yikes. His first step? He asked Claude to generate documentation for the function. Now, the initial documentation was a bit off, but it gave him a starting point. He did a bit of his own digging, then asked Claude to revise the documentation with his newfound understanding. The second time, it was much more accurate. This process of using Claude to get an initial understanding & then refining it with your own expertise is a recurring theme.
Step 2: Generate Tests (Your Safety Net)
Before you change a single line of code, you need a safety net. Unit tests are your best friend during a refactor. If you don't have good test coverage, guess what? Claude can help you write them.
Bélissent, in his refactoring journey, asked Claude to generate unit tests for the messy function. Again, the first attempt wasn't perfect. The tests were failing because Claude had misunderstood the function's purpose. But after a bit of clarification from Bélissent, Claude generated a new set of tests that passed. This is HUGE. Having a solid suite of tests gives you the confidence to make changes without breaking everything.
Step 3: The Refactoring Prompt (Be Specific!)
Now it's time to ask Claude to do the actual refactoring. But here's the thing: you can't just say "refactor this." You need to be specific. Vague prompts lead to vague (and often wrong) results.
Break down the task into smaller, manageable chunks. Instead of "refactor the entire app," try something like:
- "Refactor the file to improve readability & maintainability."
- "Go through each function in this file & move it to the appropriate file without changing its functionality."
- "Simplify this function by removing the nested statements & using a more declarative approach."
One Reddit user shared a great tip: be ULTRA specific in your instructions. They even went as far as telling Claude that if ANY functionality is not perfectly replicated after the refactor, it's a total failure. This kind of precise prompting leads to much better results.
Step 4: Review, Iterate, & Refine (The Human Touch)
This is probably the most important step. AI is a powerful tool, but it's not infallible. It can miss edge cases, make inconsistent changes, or just plain get things wrong. ALWAYS review the code that Claude generates.
This is an iterative process. Claude will propose changes, you'll review them, & then you'll provide feedback for further improvement. Maybe the refactored code is a bit oversimplified. Maybe it introduced a subtle bug. You might need to jump in & fix things yourself, or you might be able to explain the issue to Claude & have it correct its own work.
Remember, you're the one in the driver's seat. Claude is your copilot. This collaborative loop is where the real magic happens.
Advanced Techniques & Best Practices
Once you get the hang of the basic workflow, there are some more advanced techniques you can use to really level up your refactoring game.
- Incremental Execution: Don't try to refactor a massive file in one go. Break it down into smaller, incremental changes. Extract 50 lines here, 40 lines there, & run your tests after each step. This surgical approach is much safer & easier to manage.
- Leverage Different Models: Depending on your needs, you might want to switch between different Claude models. For really complex tasks, you might opt for a more powerful model like Opus.
- Use the flag for one-shot tasks: For quick, focused commands, you can use the flag to execute a single task without starting a whole conversation.
- Don't forget : If Claude seems to be getting stuck or confused, you can use the command to refresh its context & start fresh.
And when it comes to business communication & keeping track of all this, you might even consider using a tool like
Arsturn. Imagine having a custom AI chatbot trained on your project's documentation,
file, & even your chat history with Claude. New developers could ask it questions about the codebase, & it could provide instant, context-aware answers. It's a pretty cool way to keep everyone on the same page during a big refactoring project.
The Elephant in the Room: Challenges & Limitations
Now, it's not all sunshine & roses. There are definitely challenges to using AI for refactoring. For one, AI can lack the full context of a project, especially in large, multi-repo systems. It might not understand the "why" behind a certain piece of code, which could lead to it removing something that seems unused but is actually critical for a future update.
Hallucinations are another real concern. AI models can sometimes be supremely confident about a change that is completely wrong. This is why that human review step is so NON-NEGOTIABLE. A 2025 survey even found that 76% of developers have to rewrite or refactor at least half of the code that AI generates.
It's also worth noting that AI is often better at certain types of refactoring than others. It excels at repetitive tasks like updating deprecated code patterns or standardizing APIs across multiple files. But for really complex, domain-specific logic, you'll still need to rely heavily on your own expertise.
Real-World Wins: What's Possible with Claude Code?
Despite the challenges, the potential here is massive. I've seen some really cool examples of what developers are doing with Claude Code.
- From Monolith to Modular: One Reddit user successfully used Claude to split a 1400-line monolithic script into three much more manageable scripts with zero loss in functionality.
- From Jupyter Notebook to Dashboard: A developer at DeepLearning.AI used Claude to refactor a messy Jupyter notebook into a clean, interactive dashboard.
- Client Site Overhaul: A developer live-streamed their process of using Claude to refactor a client's old Next.js site, upgrading it to TypeScript & integrating a CMS.
Even the teams at Anthropic are using Claude Code internally to do things like write comprehensive tests, automate pull request comments, & help new hires get up to speed on their massive codebase.
And for businesses, this isn't just about cleaner code. It's about efficiency & innovation. When your developers aren't bogged down in tedious refactoring tasks, they have more time to build new features & solve real problems for your customers. This is where having a tool like Arsturn can also come into play. By automating customer support with a no-code AI chatbot trained on your business data, you can free up your team to focus on higher-value activities, just like Claude frees up developers to focus on higher-level design. It's all about using AI to automate the repetitive stuff so humans can focus on what they do best.
The Future is Collaborative
So, is Claude Code going to take our jobs? Honestly, no. But it is going to fundamentally change them. The future of software development is collaborative, with humans & AI working together. Tools like Claude Code are taking on the role of a hyper-competent junior developer, handling the grunt work & freeing us up to be architects, designers, & problem-solvers.
It's a pretty exciting time to be a developer. We have these incredibly powerful tools at our fingertips that can help us write better code, faster. It takes some getting used to, & you definitely need to learn how to "speak AI" to get the most out of it. But once you do, it's a total game-changer.
I hope this was helpful! I'm still learning & experimenting with this stuff myself, so I'd love to hear what you think. Have you tried using Claude Code for refactoring? What have your experiences been? Let me know in the comments.