Ask Claude to Split Large Files into Smaller, Focused Modules

Files grow until they're impossible to navigate. A controller that started simple now handles validation, business logic, email sending, and PDF generation — all in one file. Claude reads it, identifies the responsibilities, and breaks it apart.

"This OrderController is 800 lines. Split it into focused pieces."

Claude analyzes the file, groups related methods by responsibility, and extracts them into new classes — updating imports, injecting dependencies, and making sure everything still calls correctly:

# Claude might split it into:
# OrderController.php    — route handling only (thin controller)
# OrderService.php       — business logic (create, cancel, refund)
# OrderValidator.php     — custom validation rules
# OrderNotifier.php      — email and notification logic
# OrderPdfGenerator.php  — invoice/receipt generation

This works for any kind of oversized file:

# React components that do too much
"This Dashboard component is 600 lines with 5 different sections. 
Split each section into its own component."

# Utility files that became catch-alls
"utils.js has 40 unrelated functions. Group them into focused utility modules."

# Models with too much business logic
"The User model has query scopes, accessors, business methods, and event handlers. 
Extract the business logic into a UserService."

# Test files that are hard to navigate
"This test file has 50 tests covering 5 different features. 
Split it into one test file per feature."

Claude handles the tricky parts of splitting:

• Dependency management — makes sure extracted code can access what it needs via injection or imports
• Circular dependencies — avoids creating import cycles when splitting tightly coupled code
• Shared state — identifies state that multiple pieces need and decides where it should live
• Existing callers — updates every file that imports or references the original, so nothing breaks

After splitting, ask Claude to verify:

"Run the tests to make sure the split didn't break anything"

Small files with clear responsibilities are easier to read, test, and change — let Claude do the surgery on the ones that grew too large.

via Claude Code