Code Quality Metrics

Thresholds:

Cognitive Complexity

Measures how difficult code is to understand (introduced by SonarQube).

Key differences from CC:

• Penalizes nested structures more heavily
• Doesn't count all decision points equally
• Focuses on human comprehension

Calculation rules:

1. +1 for each break in linear flow (if, for, while, switch, catch, ?:)
2. +1 for each nesting level inside these structures
3. +1 for binary logical operators (&&, ||)
4. Recursion adds +1

Thresholds:

Example:

def process(items):           # 0
    for item in items:        # +1 (loop)
        if item.active:       # +1 (if) +1 (nesting=1)
            if item.valid:    # +1 (if) +2 (nesting=2)
                handle(item)
    return items              # Total: 6

Halstead Metrics

Based on counting operators and operands:

Maintainability Metrics

Maintainability Index (MI)

Composite metric combining complexity, size, and comments.

Formula: MI = 171 - 5.2 × ln(V) - 0.23 × CC - 16.2 × ln(LOC)

Thresholds:

Lines of Code (LOC)

Coupling Metrics

Afferent Coupling (Ca)

Number of classes that depend on this class.

• High Ca = Many dependents, changes are risky

Efferent Coupling (Ce)

Number of classes this class depends on.

• High Ce = Many dependencies, class is fragile

Instability (I)

I = Ce / (Ca + Ce)

• 0 = Stable (many dependents, few dependencies)
• 1 = Unstable (few dependents, many dependencies)

Cohesion Metrics

Lack of Cohesion of Methods (LCOM)

Measures how related methods are within a class.

LCOM1: Number of method pairs without shared instance variables

• 0 = Perfect cohesion
• High = Low cohesion, consider splitting

LCOM4: Number of connected components in method-field graph

• 1 = Cohesive class

• 1 = Multiple responsibilities

Quick Reference Table

Measurement Commands

ESLint Complexity

npx eslint --rule 'complexity: ["error", 10]' src/

SonarQube Analysis

sonar-scanner -Dsonar.projectKey=myproject

Python Radon

radon cc src/ -a -s  # Cyclomatic complexity
radon mi src/ -s     # Maintainability index

Additional Resources

Reference Files

For detailed measurement techniques:

• references/measurement-tools.md - Tool configurations and usage
• references/thresholds-by-language.md - Language-specific thresholds

Integration with Other Skills

Combine with:

• solid-principles for structural analysis
• refactoring-patterns for improvement strategies