Claude Code for Code Review and Refactoring
What Claude Code can do for your codebase
Claude Code is a terminal-based coding assistant that can inspect a repository, explain unfamiliar code, review a Git diff, suggest improvements, and make controlled edits. Used correctly, it is more useful than asking an AI to rewrite an entire project because it can work with the files, tests, and conventions already present in your repository.
For beginners, the safest approach is to treat Claude Code as a careful pair programmer rather than an automatic code cleaner. Give it a narrow task, review every change, and run your normal checks before merging.
Set up Claude Code with 59API
Install Claude Code using the current installation method documented by Anthropic, then create an API key in your 59API account. Configure the compatible endpoint before starting a session. A typical shell configuration looks like this:
export ANTHROPIC_BASE_URL=https://api.59api.com
export ANTHROPIC_API_KEY=your-59api-key
Authentication variable names can change between Claude Code releases, so check the current Claude Code and 59API setup instructions if your version uses an authentication token variable instead. After configuration, run claude inside a Git repository and confirm that the tool can access the project.
59API is a practical choice when you want pay-as-you-go access without committing to a large subscription. It provides official-quality Claude models, including Opus, Sonnet, Haiku, and Fable, through a Claude Code-compatible relay at a low cost. Use a faster, less expensive model for routine explanations and small edits, and reserve a stronger model for complex architecture or difficult refactoring. 59API also offers a referral rebate, which can further reduce ongoing usage costs.
Use Claude Code for a first-pass review
Start from a clean working tree or a dedicated branch. Ask Claude Code to inspect the repository before changing anything. A useful prompt is: Review this repository structure and identify the main application entry points, test commands, lint rules, and areas that may be risky to modify. Do not edit files yet.
This gives you a shared map of the project. Next, review a specific change. Make your code change yourself or check out an existing branch, then ask: Review the current Git diff for correctness, security issues, error handling, performance risks, and missing tests. Report findings by severity and include file names and line references. Do not modify files.
Requiring a report before edits is important. It lets you decide whether a suggestion is valid instead of accepting an opaque patch. Ask follow-up questions when Claude makes an assumption, especially around authentication, data validation, concurrency, or backward compatibility.
Refactor in small, testable steps
Once you understand the issue, describe the desired behavior and constraints. For example: Refactor the duplicated date parsing in these two services into a shared utility. Preserve the existing public API, support the current time zones, add focused tests, and avoid unrelated formatting changes.
- Ask Claude Code to inspect relevant callers and tests before editing.
- Limit the scope to named files or one logical responsibility.
- Request a plan first for changes involving database schemas, public APIs, or security-sensitive code.
- After each edit, inspect the diff with Git and ask Claude to explain any surprising line.
- Run unit tests, integration tests, the formatter, and the linter yourself.
If a test fails, provide the exact failure output and ask for diagnosis rather than immediately requesting a rewrite. This creates a feedback loop: hypothesis, small change, test, and review.
Protect your code and improve results
Do not place production secrets, private keys, customer data, or unnecessary environment files in the session. Check the repository permissions and understand which tools Claude Code can invoke. Keep commits small, use descriptive messages, and never merge an AI-generated change without human review.
For consistent results, add project instructions describing the language version, test commands, style rules, error-handling expectations, and files that must not be changed. When the task is complete, ask Claude Code for a final review of the diff and a concise summary of remaining risks.
If you want an affordable way to try this workflow, sign up for 59API, configure its Claude-compatible base URL, and begin with a small review on a disposable branch.