Ask Claude to Find Duplicated Code and Consolidate It into Shared Functions

Copy-paste starts as a shortcut and ends as a maintenance nightmare. When the same logic lives in five places, a bug fix in one leaves four still broken. Claude Code can find the duplicates you've forgotten about and extract them into shared code.

Search the codebase for duplicated logic — functions that do the same thing 
with slightly different names, repeated code blocks across files, and 
near-identical patterns. Extract the shared logic into reusable functions.

Claude reads across files, identifies code that does the same thing (even when variable names differ), and extracts the common pattern:

# Found duplicates:
- UserController.formatDate() and OrderController.formatDate() are identical
- Three components have the same pagination logic copy-pasted
- src/api/users.ts and src/api/orders.ts have identical error handling blocks

Then it extracts:

// Before: same logic in 3 files
// users.ts: const page = Math.max(1, parseInt(params.page) || 1);
// orders.ts: const page = Math.max(1, parseInt(query.page) || 1);
// products.ts: const page = Math.max(1, parseInt(req.page) || 1);

// After: shared utility
// src/utils/pagination.ts
export function parsePage(value: unknown): number {
  return Math.max(1, parseInt(String(value)) || 1);
}

Target specific duplication patterns:

# Find similar API clients
Compare all files in src/api/. Which ones have the same fetch wrapper, 
error handling, or retry logic? Extract the common pattern into a base client.

# Find similar components
Search for React components that render the same structure with different data. 
Can any be consolidated into a single parameterised component?

# Find similar validation
Check if multiple forms validate the same fields the same way. 
Extract shared validation rules into a central schema.

# Find similar test setup
Look for test files that have identical beforeEach blocks or helper functions.
Extract the common setup into shared test utilities.

Duplication is the root of inconsistency — let Claude find the copies and consolidate them into a single source of truth.

via Claude Code