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

Priority

Category

Impact

Prefix

1

Structure & Decomposition

CRITICAL

struct-

2

Coupling & Dependencies

CRITICAL

couple-

3

Naming & Clarity

HIGH

name-

4

Conditional Logic

HIGH

cond-

5

Abstraction & Patterns

MEDIUM-HIGH

pattern-

6

Data Organization

MEDIUM

data-

7

Error Handling

MEDIUM

error-

8

Micro-Refactoring

LOW

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