Introduction

Most refactors go wrong long before the first line of code is changed.

They fail in planning.

You open a big file, see some messy logic, and think, "I’ll just clean this up real quick." Two hours later you’re juggling failing tests, broken dependencies, and a half-finished rewrite you’re scared to ship.

A simple habit can dramatically reduce that risk: write a checklist-first refactor.

Instead of starting with code, you start with a step-by-step checklist, broken down by file and by change, aligned with how you’ll test and verify each step. You treat that checklist as the single source of truth throughout the refactor.

This post walks through why this works, how to do it, and how to turn your refactoring checklists into living, reusable tools that elevate your team’s engineering practice over time.

Why Checklist-First Refactoring Works

Refactoring is inherently risky because you’re changing behavior-less code paths in complex systems. The problems usually aren’t in our abilities—they’re in our process:

• We take on too much at once.
• We refactor without clear goals beyond “clean it up.”
• We don’t align changes with verification steps.
• We forget non-functional improvements like readability and performance.

A checklist-first approach fixes this by:

1. Externalizing thinking – You design the refactor in text, not in your head.
2. Constricting scope – You’re forced to break work into small, testable steps.
3. Clarifying intent – Each step has a purpose and a validation strategy.
4. Making best practices explicit – You embed SOLID, patterns, and performance considerations into the checklist itself.
5. Enabling reuse – Once written, a good refactor checklist can be reused, refined, and shared.

Think of it as doing the architectural thinking in Markdown before you touch the bricks.

Step 1: Write the Checklist Before You Touch Code

Open a .md file—refactor-checklist.md—and describe the change in steps. Start with:

• Context: What’s wrong with the current design? (e.g., God object, circular deps, duplication)
• Goals: What should be better when this is done?
• Non-goals: What are you explicitly not changing to avoid scope creep?

Then, break down the refactor by file and step.

Example structure:

# Refactor: Extract PaymentStrategy from OrderService

## Context
OrderService has too many responsibilities: validation, payment processing, notifications.

## Goals
- Improve readability by separating payment logic
- Make adding new payment methods easy (extensibility)
- Reduce risk with small, testable steps

## Non-Goals
- No change to notification system
- No changes to API contracts

---

## Plan by File and Step

### Step 1: Add PaymentStrategy interface
- [ ] Create `PaymentStrategy` interface in `payment/PaymentStrategy.ts`
- [ ] Define `charge(amount, paymentDetails): PaymentResult`
- [ ] Add unit tests for the interface contract (doc tests or example implementations)

### Step 2: Implement CreditCardPaymentStrategy
- [ ] Create `CreditCardPaymentStrategy` in `payment/CreditCardPaymentStrategy.ts`
- [ ] Move credit card logic from `OrderService` into this class
- [ ] Write unit tests for `CreditCardPaymentStrategy`

### Step 3: Wire strategy into OrderService (without removing old code yet)
- [ ] Inject `PaymentStrategy` dependency into `OrderService`
- [ ] Add feature flag or config switch for using the strategy
- [ ] Add tests verifying behavior unchanged when flag is on

### Step 4: Remove duplicate payment logic
- [ ] Delete old payment logic from `OrderService`
- [ ] Run regression tests and compare behavior

### Step 5: Cleanup and documentation
- [ ] Update architecture docs to describe new payment strategy
- [ ] Add notes on how to add a new payment method

The important part: you do all of this before any code changes. You’re designing the journey.

Step 2: Treat the Checklist as the Single Source of Truth

Once you start coding, the checklist becomes your refactor contract:

• You don’t add surprise steps in the code without updating the list.
• You only check off an item when:
  • The code change is complete, and
  • It passes the tests you planned for it.

This discipline has several benefits:

• Traceability – You can answer, “What changed, where, and why?” at any time.
• Reviewability – Code reviewers can follow the checklist commit by commit.
• Stop points – You can pause safely between items, knowing the system is stable.

A practical pattern:

• One checklist section → one logical commit or PR.
• Item check-off → tests green + review done.

Your Markdown file becomes a living change log and safety net.

Step 3: Keep Refactors Incremental and Small

Refactors go off the rails when they try to do everything.

Checklist-first forces you to think incrementally:

• Can this change be split into introduce and remove phases?
• Can we add new code in parallel with existing code before cutting over?
• Can each step be implemented, reviewed, and verified independently?

Common incremental patterns to capture in your checklist:

1. Branch-by-abstraction

   • Step 1: Introduce abstraction (interface/adapter) but keep old path.
   • Step 2: Wire some clients to the new abstraction.
   • Step 3: Migrate all clients.
   • Step 4: Remove old implementation.

2. Strangler pattern (for modules/services)

   • Step 1: Introduce new module alongside old.
   • Step 2: Route some use cases to new module.
   • Step 3: Gradually reroute all traffic.
   • Step 4: Delete old module.

Each step in your refactor plan should:

• Touch as few files as possible.
• Have a clear rollback plan.
• Be safe to stop after, with the system still functioning.

If a checklist item feels too big or risky, split it before you start coding.

Step 4: Align the Checklist with Your Testing Approach

A refactor isn’t done when the code compiles; it’s done when behavior is verified.

Every checklist item should include how it will be validated. Explicitly declare the testing strategy:

• TDD / Red-Green-Refactor
  • Add a failing test first.
  • Implement the minimal change to pass it.
  • Cleanup while keeping tests green.
• BDD / Scenario-based
  • Define user scenarios (Given-When-Then).
  • Ensure each refactor step keeps these scenarios green.

Example:

### Step 3: Wire strategy into OrderService
- [ ] Add integration test: `OrderService charges via injected PaymentStrategy`
  - Red: write test, see it fail with current implementation
  - Green: inject `PaymentStrategy` and adapt code
  - Refactor: inline cleanup and remove duplication
- [ ] Run full payment-related regression test suite

This alignment gives you:

• Confidence that refactors don’t silently break behavior.
• A natural rhythm: checklist step → tests → green → check off.

Step 5: Encode Best Practices Directly into the Checklist

Checklists aren’t just for what to change, but also how to change.

Use them to embed design principles:

• SOLID
  • Single Responsibility: “After this step, this class should have only one reason to change.”
  • Open/Closed: “New payment methods added via new strategies, not conditionals.”
• Design patterns
  • Strategy, Factory, Adapter, Decorator, etc.
• Performance considerations
  • “Measure latency before/after change.”
  • “Avoid additional DB round trips in this path.”

Example snippet:

### Design & Quality Checklist (applies to all steps)
- [ ] SRP: Each class touched has a single clear responsibility
- [ ] No new static/global coupling introduced
- [ ] Dependencies point inward (toward domain), not outward
- [ ] New abstractions are tested at their boundaries
- [ ] No performance regressions in hot paths (compare metrics if available)

By making these explicit, you:

• Avoid “refactors” that just move code around.
• Ensure each change nudges the system toward better architecture.

Step 6: Make Non-Functional Goals First-Class Citizens

Refactors often claim to improve readability or extensibility, but those goals stay vague.

Make them concrete in your checklist:

• Readability
  • Method names describe what, not how.
  • Functions/classes under X lines.
  • Complex logic extracted to well-named helpers.
• Extensibility
  • New feature X can be added without modifying existing core logic.
  • Swapping implementation Y requires changing only one module.
• Performance
  • No additional network calls added to critical path.
  • Memory usage remains within acceptable bounds.

You can even add a “before/after” reflection step:

### Final Non-Functional Review
- [ ] Is this easier to understand for a new teammate?
- [ ] Is it easier to plug in a new payment method now?
- [ ] Did we avoid adding unnecessary complexity?

If you can’t answer these positively, the refactor may not be worth merging yet.

Step 7: Reuse and Refine Checklists as Living Documents

The real power comes when your checklists stop being one-off artifacts and become reusable tools.

Patterns to adopt:

1. Create a /doc/refactoring/ folder in your repo.
2. Start with templates, like:
   • extract-class-refactor-template.md
   • module-strangulation-template.md
   • performance-sensitive-refactor-template.md
3. After each refactor, update the template with:
   • Things that went well.
   • Pitfalls you hit.
   • New best practices learned.

Example:

# Template: Extract Class Refactor

## Pre-checks
- [ ] Existing behavior covered by tests? If not, add characterization tests.
- [ ] Identify owners/stakeholders for this code.

## Steps
- [ ] Identify cohesive responsibilities to extract
- [ ] Define new class interface
- [ ] Move logic incrementally, keep tests passing
- [ ] Replace old usage sites
- [ ] Remove dead code

## Post-checks
- [ ] Review for SRP and clear naming
- [ ] Run full test suite
- [ ] Capture any new learnings in this template

Over time, your team builds a refactoring playbook tailored to your architecture and constraints.

Conclusion

Refactoring is never risk-free, but it can be disciplined and predictable.

By writing a detailed checklist before touching any code, you:

• Break work down by file and step.
• Keep changes incremental and small in scope.
• Tie every step to a testing and validation strategy.
• Encode SOLID principles, patterns, and performance concerns into the process.
• Make non-functional improvements explicit and measurable.
• Build reusable, evolving checklists that make your future refactors safer and faster.

Next time you’re tempted to “just clean it up real quick,” pause.

Open a Markdown file.

Write the checklist.

Then let the code follow, one safe, deliberate step at a time.