Claude Code Planning - 2026

Planning Skill for Large-Scale Refactoring

Large-scale refactoring without a plan is how codebases die. Before you rename that core function or restructure that module, use Claude Code to map dependencies, plan the migration order, and validate each step. Here is how to do it right.

Refactoring Planning Dependency Analysis Incremental Migration

The Problem with Unplanned Refactoring

Large refactoring fails in predictable ways. You rename a function. Three files still call the old name. You fix those. Now something downstream breaks. You fix that. Thirty minutes later you are deep in a rabbit hole of cascading fixes and wondering why you started.

The root cause: refactoring is a tree traversal problem, not a linear search. Code has dependencies. When you change a leaf, you must update its parent. When you update the parent, you may affect siblings. Without mapping this first, you are guessing.

The solution: plan the refactoring as a dependency-ordered sequence of changes. Claude Code can help map these dependencies accurately.

Step 1: Map the Dependency Graph

Before changing anything, ask Claude to analyze the scope of the proposed change:

I want to refactor the authenticateUser function in auth/service.js.
1. Find all files that call authenticateUser
2. Find all files that call functions which authenticateUser calls
3. Identify which call sites are in production code vs tests
4. Map the dependency tree from this function outward

Show me the full list of files that will need updating if I rename or change this function signature.

Claude will trace the call graph and give you the complete set of files that need updating. This is the migration map - do not proceed until you have it.

Step 2: Order the Changes

With the dependency map, plan the change order. The rule: work from leaves toward roots. Change the deepest dependencies first, then update their callers, then the callers of those callers:

Step 1: Change the core function itself (rename, restucture, or reimplement)
Step 2: Update all direct callers
Step 3: Update indirect callers (callers of the direct callers)
Step 4: Continue until you reach the entry points

For each step: make the change, run the tests, verify behavior is preserved. Only proceed to the next step when the current one passes.

This ordered approach means each intermediate state is a working system. If something breaks, you know exactly which step introduced it.

Step 3: Write the Migration Script

For large refactoring, write a step-by-step migration script that Claude Code follows:

## Migration: Rename authenticateUser to createUserSession

Phase 1:
- Edit auth/service.js: rename function to createUserSession
- Edit auth/middleware.js: update the import and call site
- Run tests: npm test -- --testPathPattern=auth
- Verify: auth flows still work in staging

Phase 2:
- Edit users/profile.js: update call site
- Edit payments/checkout.js: update call site
- Run tests: npm test -- --testPathPattern="users|payments"
- Verify: user profile and checkout flows work

Phase 3:
- Edit api/v1/auth.js: update remaining call sites
- Run full test suite: npm test
- Verify: all tests pass

Do not proceed to Phase 2 until Phase 1 tests pass.

Having the script as a document means you can stop and resume without losing your place. Each phase is a self-contained unit that preserves functionality.

Step 4: Validate at Each Step

The critical discipline: validate after each incremental change. What to check:

Tests pass - Not just that they run, but that assertions actually exercise the changed code
Behavior preserved - Manually walk through the user flow in staging or locally
Type checking - If using TypeScript, run the type checker after each change
No dead code introduced - The old function should have no remaining call sites before you remove it

If tests fail at any step, stop and fix before proceeding. Large refactoring only works when every intermediate state is a working system.

Common Refactoring Patterns

Pattern	Risk	Mitigation
Rename function	Breaks all call sites	Use IDE refactor tool + update all call sites in dependency order
Split large function	Loses context, changes call signature	Extract new functions first, update call sites, then remove old logic
Move function between modules	Import paths break, circular deps	Update imports in target module first, then all callers, then delete original
Change data structure	All consumers need updating	Deprecate old structure, add new structure, update consumers one by one

Plan before you refactor

Use Claude Code dependency analysis before starting any large refactoring. The upfront investment in planning saves hours of debugging.

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Frequently Asked Questions

Why is planning critical for large refactoring?

Large refactoring changes the structure of code that other code depends on. Without a plan, you risk breaking dependent code, losing track of what changed, and accumulating hidden bugs that only surface in production. A solid plan identifies all dependent code first, defines the migration order, and sets validation checkpoints before you touch production-critical paths. The cost of planning is small compared to debugging an unplanned migration.

How does Claude Code help with refactoring planning?

Claude Code reads and understands your entire codebase. It can identify all files that use a function being renamed, trace dependency chains, and map the blast radius of proposed changes. This gives you an accurate migration map before you write a single line of new code. Ask Claude to trace specific functions or modules - it will give you a comprehensive dependency report in seconds.

What makes a refactoring plan work in production?

Three things make a refactoring plan reliable: accurate dependency mapping (knowing what depends on what), incremental changes (small PRs that preserve functionality), and validation at each step (tests pass, app runs). The plan must account for the order of changes - you refactor leaves of the dependency tree first, then work inward toward the roots. This way each intermediate state is a working system.

How do I validate a refactoring went correctly?

Run your test suite after each incremental change. Check that the behavior is preserved - not just that tests pass, but that actual runtime behavior matches expectations. Use feature flags to run新旧 code side by side if needed for critical paths. Log and monitor error rates in production after deployment. If any test fails or behavior differs, stop immediately and diagnose before proceeding to the next step.