Fowler/Martin Code Refactoring Best Practices

Comprehensive code refactoring guide based on Martin Fowler's catalog and Clean Code principles, designed for AI agents and LLMs. Contains 43 rules across 8 categories, prioritized by impact to guide automated refactoring and code generation.

When to Apply

Reference these guidelines when:

• Refactoring existing code to improve maintainability
• Decomposing long methods or large classes
• Reducing coupling between components
• Simplifying complex conditional logic
• Reviewing code for code smells and anti-patterns

Rule Categories by Priority

struct-

couple-

name-

cond-

pattern-

data-

error-

micro-

Quick Reference

1. Structure & Decomposition (CRITICAL)

• struct-extract-method

  - Extract Method for Long Functions

• struct-single-responsibility

  - Apply Single Responsibility Principle

• struct-extract-class

  - Extract Class from Large Class

• struct-compose-method

  - Compose Method for Readable Flow

• struct-function-length

  - Keep Functions Under 20 Lines

• struct-replace-method-with-object

  - Replace Method with Method Object

• struct-parameter-object

  - Introduce Parameter Object

2. Coupling & Dependencies (CRITICAL)

• couple-dependency-injection

  - Use Dependency Injection

• couple-hide-delegate

  - Hide Delegate to Reduce Coupling

• couple-remove-middle-man

  - Remove Middle Man When Excessive

• couple-feature-envy

  - Fix Feature Envy by Moving Methods

• couple-interface-segregation

  - Apply Interface Segregation Principle

• couple-preserve-whole-object

  - Preserve Whole Object Instead of Fields

3. Naming & Clarity (HIGH)

• name-intention-revealing

  - Use Intention-Revealing Names

• name-avoid-abbreviations

  - Avoid Abbreviations and Acronyms

• name-consistent-vocabulary

  - Use Consistent Vocabulary

• name-searchable-names

  - Use Searchable Names

• name-avoid-encodings

  - Avoid Type Encodings in Names

4. Conditional Logic (HIGH)

• cond-guard-clauses

  - Replace Nested Conditionals with Guard Clauses

• cond-polymorphism

  - Replace Conditional with Polymorphism

• cond-decompose

  - Decompose Complex Conditionals

• cond-consolidate

  - Consolidate Duplicate Conditional Fragments

• cond-special-case

  - Introduce Special Case Object

• cond-lookup-table

  - Replace Conditional with Lookup Table

5. Abstraction & Patterns (MEDIUM-HIGH)

• pattern-strategy

  - Extract Strategy for Algorithm Variants

• pattern-template-method

  - Use Template Method for Shared Skeleton

• pattern-factory

  - Use Factory for Complex Object Creation

• pattern-open-closed

  - Apply Open-Closed Principle

• pattern-composition-over-inheritance

  - Prefer Composition Over Inheritance

• pattern-extract-superclass

  - Extract Superclass for Common Behavior

6. Data Organization (MEDIUM)

• data-encapsulate-collection

  - Encapsulate Collection

• data-replace-primitive

  - Replace Primitive with Object

• data-encapsulate-record

  - Encapsulate Record into Class

• data-split-variable

  - Split Variable with Multiple Assignments

• data-replace-temp-with-query

  - Replace Temp with Query

7. Error Handling (MEDIUM)

• error-exceptions-over-codes

  - Use Exceptions Instead of Error Codes

• error-custom-exceptions

  - Create Domain-Specific Exception Types

• error-fail-fast

  - Fail Fast with Preconditions

• error-separate-concerns

  - Separate Error Handling from Business Logic

8. Micro-Refactoring (LOW)

• micro-remove-dead-code

  - Remove Dead Code

• micro-inline-variable

  - Inline Trivial Variables

• micro-simplify-expressions

  - Simplify Boolean Expressions

• micro-rename-for-clarity

  - Rename for Clarity

How to Use

Read individual reference files for detailed explanations and code examples:

• Section definitions - Category structure and impact levels
• Rule template - Template for adding new rules
• Individual rules:

  references/{prefix}-{slug}.md

Full Compiled Document

For the complete guide with all rules expanded:

AGENTS.md