code-documentation

name	code-documentation
description	Guidelines for self-explanatory code and meaningful documentation. Activate when working with comments, docstrings, documentation, code clarity, API documentation, JSDoc, or discussing code commenting strategies. Guides on why over what, anti-patterns, decision frameworks, and language-specific examples.

Code Documentation & Self-Explanatory Code

Auto-activate when: User discusses comments, documentation, docstrings, code clarity, code quality, API docs, JSDoc, Python docstrings, or asks about commenting strategies.

Core Principle

Write code that speaks for itself. Comment only when necessary to explain WHY, not WHAT.

Most code does not need comments. Well-written code with clear naming and structure is self-documenting.

The best comment is the one you don't need to write because the code is already obvious.

---

The Commenting Philosophy

When to Comment

✅ DO comment when explaining:

• WHY something is done (business logic, design decisions)
• Complex algorithms and their reasoning
• Non-obvious trade-offs or constraints
• Workarounds for bugs or limitations
• API contracts and public interfaces
• Regex patterns and what they match
• Performance considerations or optimizations
• Constants and magic numbers
• Gotchas or surprising behaviors

❌ DON'T comment when:

• The code is obvious and self-explanatory
• The comment repeats the code (redundant)
• Better naming would eliminate the need
• The comment would become outdated quickly
• It's decorative or organizational noise
• It states what a standard language construct does

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Comment Anti-Patterns

❌ 1. Obvious Comments

BAD:

counter = 0  # Initialize counter to zero
counter += 1  # Increment counter by one
user_name = input("Enter name: ")  # Get user name from input

Better: No comment needed - the code is self-explanatory.

---

❌ 2. Redundant Comments

BAD:

def get_user_name(user):
    return user.name  # Return the user's name

def calculate_total(items):
    # Loop through items and sum the prices
    total = 0
    for item in items:
        total += item.price
    return total

Better:

def get_user_name(user):
    return user.name

def calculate_total(items):
    return sum(item.price for item in items)

---

❌ 3. Outdated Comments

BAD:

# Calculate tax at 5% rate
tax = price * 0.08  # Actually 8%, comment is wrong

# DEPRECATED: Use new_api_function() instead
def old_function():  # Still being used, comment is misleading
    pass

Better: Keep comments in sync with code, or remove them entirely.

---

❌ 4. Noise Comments

BAD:

# Start of function
def calculate():
    # Declare variable
    result = 0
    # Return result
    return result
# End of function

Better: Remove all of these comments.

---

❌ 5. Dead Code & Changelog Comments

BAD:

# Don't comment out code - use version control
# def old_function():
#     return "deprecated"

# Don't maintain history in comments
# Modified by John on 2023-01-15
# Fixed bug reported by Sarah on 2023-02-03

Better: Delete the code. Git has the history.

---

Good Comment Examples

✅ Complex Business Logic

# Apply progressive tax brackets: 10% up to $10k, 20% above
# This matches IRS publication 501 for 2024
def calculate_progressive_tax(income):
    if income <= 10000:
        return income * 0.10
    else:
        return 1000 + (income - 10000) * 0.20

✅ Non-obvious Algorithms

# Using Floyd-Warshall for all-pairs shortest paths
# because we need distances between all nodes.
# Time: O(n³), Space: O(n²)
for k in range(vertices):
    for i in range(vertices):
        for j in range(vertices):
            dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j])

✅ Regex Patterns

# Match email format: [e-mail]
# Allows letters, numbers, dots, hyphens in username
# Requires valid domain and 2+ char extension
email_pattern = r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$'

✅ API Constraints or Gotchas

# GitHub API rate limit: 5000 requests/hour for authenticated users
# We implement exponential backoff to handle rate limiting
await rate_limiter.wait()
response = await fetch(github_api_url)

✅ Workarounds for Bugs

# HACK: Workaround for bug in library v2.1.0
# Remove after upgrading to v2.2.0
# See: https://github.com/library/issues/123
if library_version == "2.1.0":
    apply_workaround()

---

Decision Framework

Before writing a comment, ask yourself:

Step 1: Is the code self-explanatory?

• If YES → No comment needed
• If NO → Continue to step 2

Step 2: Would a better variable/function name eliminate the need?

• If YES → Refactor the code instead
• If NO → Continue to step 3

Step 3: Does this explain WHY, not WHAT?

• If explaining WHAT → Refactor code to be clearer
• If explaining WHY → Good comment candidate

Step 4: Will this help future maintainers?

• If YES → Write the comment
• If NO → Skip it

---

Special Cases for Comments

Public APIs and Docstrings

Python Docstrings

def calculate_compound_interest(
    principal: float,
    rate: float,
    time: int,
    compound_frequency: int = 1
) -> float:
    """
    Calculate compound interest using the standard formula.

    Args:
        principal: Initial amount invested
        rate: Annual interest rate as decimal (e.g., 0.05 for 5%)
        time: Time period in years
        compound_frequency: Times per year interest compounds (default: 1)

    Returns:
        Final amount after compound interest

    Raises:
        ValueError: If any parameter is negative

    Example:
        >>> calculate_compound_interest(1000, 0.05, 10)
        1628.89
    """
    if principal < 0 or rate < 0 or time < 0:
        raise ValueError("Parameters must be non-negative")

    # Compound interest formula: A = P(1 + r/n)^(nt)
    return principal * (1 + rate / compound_frequency) ** (compound_frequency * time)

JavaScript/TypeScript JSDoc

/**
 * Fetch user data from the API.
 *
 * @param {string} userId - The unique user identifier
 * @param {Object} options - Configuration options
 * @param {boolean} options.includeProfile - Include profile data (default: true)
 * @param {number} options.timeout - Request timeout in ms (default: 5000)
 *
 * @returns {Promise<User>} User object with requested fields
 *
 * @throws {Error} If userId is invalid or request fails
 *
 * @example
 * const user = await fetchUser('123', { includeProfile: true });
 */
async function fetchUser(userId, options = {}) {
  // Implementation
}

---

Constants and Configuration

# Based on network reliability studies (95th percentile)
MAX_RETRIES = 3

# AWS Lambda timeout is 15s, leaving 5s buffer for cleanup
API_TIMEOUT = 10000  # milliseconds

# Cache duration optimized for balance between freshness and load
# See: docs/performance-tuning.md
CACHE_TTL = 300  # 5 minutes

---

Annotations for TODOs and Warnings

# TODO: Replace with proper authentication after security review
# Issue: #456
def temporary_auth(user):
    return True

# WARNING: This function modifies the original array instead of creating a copy
def sort_in_place(arr):
    arr.sort()
    return arr

# FIXME: Memory leak in production - investigate connection pooling
# Ticket: JIRA-789
def get_connection():
    return create_connection()

# PERF: Consider caching this result if called frequently in hot path
def expensive_calculation(data):
    return complex_algorithm(data)

# SECURITY: Validate input to prevent SQL injection before using in query
def build_query(user_input):
    sanitized = escape_sql(user_input)
    return f"SELECT * FROM users WHERE name = '{sanitized}'"

Common Annotation Keywords

• TODO: - Work that needs to be done
• FIXME: - Known bugs that need fixing
• HACK: - Temporary workarounds
• NOTE: - Important information or context
• WARNING: - Critical information about usage
• PERF: - Performance considerations
• SECURITY: - Security-related notes
• BUG: - Known bug documentation
• REFACTOR: - Code that needs refactoring
• DEPRECATED: - Soon-to-be-removed code

---

Refactoring Over Commenting

Instead of Commenting Complex Code...

BAD: Complex code with comment

# Check if user is admin or has special permissions
if user.role == "admin" or (user.permissions and "special" in user.permissions):
    grant_access()

...Extract to Named Function

GOOD: Self-explanatory through naming

def user_has_admin_access(user):
    return user.role == "admin" or has_special_permission(user)

def has_special_permission(user):
    return user.permissions and "special" in user.permissions

if user_has_admin_access(user):
    grant_access()

---

Language-Specific Examples

JavaScript

// Good: Explains WHY we debounce
// Debounce search to reduce API calls (500ms wait after last keystroke)
const debouncedSearch = debounce(searchAPI, 500);

// Bad: Obvious
let count = 0;  // Initialize count to zero
count++;  // Increment count

// Good: Explains algorithm choice
// Using Set for O(1) lookup instead of Array.includes() which is O(n)
const seen = new Set(ids);

Python

# Good: Explains the algorithm choice
# Using binary search because data is sorted and we need O(log n) performance
index = bisect.bisect_left(sorted_list, target)

# Bad: Redundant
def get_total(items):
    return sum(items)  # Return the sum of items

# Good: Explains why we're doing this
# Extract to separate function for type checking in mypy
def validate_user(user):
    if not user or not user.id:
        raise ValueError("Invalid user")
    return user

TypeScript

// Good: Explains the type assertion
// TypeScript can't infer this is never null after the check
const element = document.getElementById('app') as HTMLElement;

// Bad: Obvious
const sum = a + b;  // Add a and b

// Good: Explains non-obvious behavior
// spread operator creates shallow copy; use JSON for deep copy
const newConfig = { ...config };

---

Comment Quality Checklist

Before committing, ensure your comments:

• Explain WHY, not WHAT
• Are grammatically correct and clear
• Will remain accurate as code evolves
• Add genuine value to code understanding
• Are placed appropriately (above the code they describe)
• Use proper spelling and professional language
• Follow team conventions for annotation keywords
• Could not be replaced by better naming or structure
• Are not obvious statements about language features
• Reference tickets/issues when applicable

---

Summary

Priority order:

1. Clear code - Self-explanatory through naming and structure
2. Good comments - Explain WHY when necessary
3. Documentation - API docs, docstrings for public interfaces
4. No comments - Better than bad comments that lie or clutter

Remember: Comments are a failure to make the code self-explanatory. Use them sparingly and wisely.

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Key Takeaways

Goal	Approach
Reduce comments	Improve naming, extract functions, simplify logic
Improve clarity	Use self-explanatory code structure, clear variable names
Document APIs	Use docstrings/JSDoc for public interfaces
Explain WHY	Comment only business logic, algorithms, workarounds
Maintain accuracy	Update comments when code changes, or remove them