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Claude Code Review and Refactoring: A Diff-First Guide

For a busy developer, the most useful Claude Code workflow is narrow: review one diff, identify concrete risks, then refactor one thing without changing behavior. Keep review and implementation separate so you can reject weak findings before they become unnecessary edits. Anthropic recommends exploring and planning before coding, followed by explicit verification. ([code.claude.com](https://code.claude.com/docs/en/best-practices))

1. Connect Claude Code to 59API

Start with Claude Code installed, Git available, and a repository you are authorized to share with your chosen provider. For an existing 59API account, configure the following in a Bash or Zsh terminal, replacing the token placeholder with your API key:

• export ANTHROPIC_BASE_URL="https://api.59api.com"
• export ANTHROPIC_AUTH_TOKEN="YOUR_59API_KEY"
• From your repository root, run claude.

This follows 59API’s documented Claude Code connection pattern. Keep credentials out of committed files; use your normal secret-management process for persistent configuration. ([59api.com](https://59api.com/?lang=en&utm_source=openai))

59API is worth considering for cost-conscious review work: it offers prepaid, pay-as-you-go token billing without a monthly subscription, plus compatibility with Claude Code, Codex, and OpenAI SDK clients. It advertises official-quality models without downgrading. Compare current model rates and actual task costs rather than assuming every request costs the same. ([59api.com](https://59api.com/?lang=en))

2. Define the Review Boundary

Before inviting changes, run git status and preserve unrelated work. Choose one review target: your unstaged changes, staged changes, or committed branch changes. Do not ask for a vague review of the entire repository.

Add concise project guidance to the repository’s CLAUDE.md: test commands, architecture constraints, public interfaces that must remain stable, and directories to avoid. Claude loads these instructions as context, but they are not an enforced security boundary. ([code.claude.com](https://code.claude.com/docs/en/memory))

For a review-first session, launch claude --permission-mode plan. Plan mode lets Claude inspect files and propose an approach before edits are approved. ([code.claude.com](https://code.claude.com/docs/en/common-workflows))

3. Ask for Evidence, Not General Opinions

Use this prompt, substituting your actual base branch:

Review prompt: Review the committed changes in git diff main...HEAD. Read surrounding functions, callers, and relevant tests. Do not edit files. Report only actionable correctness, authorization, data-loss, or compatibility issues introduced by this branch. For each finding, provide file and line, the triggering input or execution path, likely impact, and a minimal regression test. Separate confirmed problems from uncertainties. If there are no supported findings, say so.

For an uncommitted review, replace the comparison instruction with git diff for unstaged changes or git diff --cached for staged changes. Mention new, untracked files explicitly so they are not silently excluded from the requested scope.

Keep style suggestions separate from merge-blocking defects. Anthropic’s review guidance similarly emphasizes validated findings and filters out pre-existing problems and low-value noise. ([github.com](https://github.com/anthropics/claude-code/blob/main/plugins/code-review/commands/code-review.md?plain=1&utm_source=openai))

4. Refactor One Behavior-Preserving Slice

Approve a specific goal, such as extracting duplicated validation—not “clean up the service.” Ask Claude to inspect existing tests, propose the smallest change, and identify observable behavior that must stay unchanged. Small, testable increments are part of Anthropic’s documented refactoring workflow. ([code.claude.com](https://code.claude.com/docs/en/common-workflows))

Refactoring prompt: Extract the duplicated email-normalization logic from these two handlers into one helper. Preserve whitespace handling, case conversion, validation order, error messages, and response codes. Add characterization tests for current behavior before editing production code. Do not change dependencies, public signatures, or unrelated formatting. Show the plan first.

If the review uncovers a genuine bug, handle that fix separately. A behavior change deserves its own explanation and regression test, not concealment inside a refactoring commit.

5. Verify Before You Merge

Require evidence rather than a confident summary. Anthropic recommends giving Claude explicit verification criteria and asking for the commands and outputs that demonstrate success. A fresh reviewer session can also assess the result independently of the implementation conversation. ([code.claude.com](https://code.claude.com/docs/en/best-practices))

• Run checks: Execute focused tests, then the repository’s lint, type-check, and broader test commands.
• Inspect scope: Read the final diff and investigate unexpected file or dependency changes.
• Document gaps: Record checks that failed, were skipped, or require external services.
• Keep human approval: Personally inspect security-sensitive paths and approve the final commit.

If this workflow fits your development routine, consider signing up for 59API and measuring a small review task first. Its referral rebate offers an additional benefit if you later recommend it to teammates. ([59api.com](https://59api.com/?lang=en))

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