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Claude Code Review & Refactoring: A 2026 Playbook

Separate Review From Implementation

For your 2026 Claude Code workflow, establish three distinct checkpoints: investigate the change, approve a narrowly scoped refactor, and verify the result. This follows Anthropic's recommended separation of exploration, planning, and implementation rather than asking an agent to review and rewrite everything at once. ([code.claude.com](https://code.claude.com/docs/en/best-practices))

1. Establish Repository Rules and a Baseline

Run /init to generate a starter CLAUDE.md, then edit it down to useful project instructions. Include actual test commands, architectural boundaries, compatibility requirements, and prohibited changes. Claude reads this file as persistent project context; keep it concise rather than turning it into exhaustive documentation. ([code.claude.com](https://code.claude.com/docs/en/best-practices))

• Before editing: inspect git status and preserve unrelated work.
• Define invariants: public signatures, response formats, ordering, and error behavior must remain unchanged.
• Record the baseline: run the relevant tests and identify existing failures separately.

Treat these as your working checklist, not permission to clean up every issue discovered. Anthropic recommends small, testable refactoring increments and explicit backward-compatibility requirements. ([code.claude.com](https://code.claude.com/docs/en/common-workflows))

2. Review an Explicit Diff

In current Claude Code versions, /code-review reviews branch changes and uncommitted work. For a precise comparison, use /code-review main...my-feature, replacing the branch names. A path such as /code-review src/auth can narrow the target. This local workflow is distinct from Anthropic's managed GitHub Code Review service. ([code.claude.com](https://code.claude.com/docs/en/code-review-local))

For a tailored review, give Claude this prompt:

Review the changes against main without editing. Read affected callers and tests. Prioritize authorization failures, incorrect state transitions, concurrency, and compatibility regressions. For each finding, provide file and line, triggering input, expected versus actual behavior, and a reproduction test. Separate confirmed defects from hypotheses.

Use the report-only workflow first. The --fix flag additionally asks Claude to apply findings; omit it until you have evaluated the evidence. ([code.claude.com](https://code.claude.com/docs/en/code-review-local))

3. Turn Findings Into a Bounded Refactoring Plan

Start an investigation with claude --permission-mode plan. Plan mode supports exploration without source-file edits. Use it to understand dependencies and agree on the change boundary before implementation. ([code.claude.com](https://code.claude.com/docs/en/permissions))

For example:

Plan how to extract duplicate retry logic from the payment clients. Preserve retry counts, timeout behavior, exception types, and request idempotency. List affected files, callers, risks, and tests. Do not introduce dependencies or change public interfaces.

Approve one coherent change at a time: extract a helper, verify it, then consider the next improvement. Keep behavior-changing bug fixes separate from structural cleanup so each can be reviewed against its own acceptance criteria. ([code.claude.com](https://code.claude.com/docs/en/common-workflows))

4. Prove Behavior Before and After Editing

Ask Claude to inspect existing tests, identify missing edge cases, and add tests using the repository's established framework and assertion style. Then run those tests before refactoring and repeat them afterward. Anthropic's workflow explicitly supports generating edge-case tests and verifying refactored code. ([code.claude.com](https://code.claude.com/docs/en/common-workflows))

For the retry example, specify your own acceptance cases: immediate success, success after one failure, exhaustion, timeout, and a non-retryable error. Request exact commands, exit results, and remaining failures—not simply “tests pass.” Finish with a fresh review session that examines the diff and tries to disprove the implementation's correctness. ([code.claude.com](https://code.claude.com/docs/en/best-practices))

5. Keep Permissions and Data Exposure Deliberate

Review permissions through /permissions rather than broadly bypassing safeguards. Approve only the commands needed for the task. Before routing proprietary code through any relay, check your organization's data-handling requirements: Anthropic explicitly states that it does not audit or endorse third-party gateway products. ([code.claude.com](https://code.claude.com/docs/en/permissions))

6. Lower Review Costs With 59API

59API is a strong low-cost option for developers who want prepaid, pay-as-you-go Claude access without committing to a monthly subscription. It supports Claude Code, Codex, and OpenAI SDK clients, alongside Claude and GPT models. The provider describes its service as delivering native official-quality models without downgrading them, and offers a referral rebate. Compare current model and cache rates against your actual workload rather than assuming a universal savings percentage. ([59api.com](https://59api.com/?lang=en))

Its Claude Code setup uses ANTHROPIC_BASE_URL and ANTHROPIC_AUTH_TOKEN; copy the endpoint from its setup documentation and keep your key out of version control. If you want an economical starting point, consider signing up for 59API and measuring the cost of one representative review-and-refactor cycle. ([59api.com](https://59api.com/?lang=en))

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