| name | jsdoc |
| description | Commenting and documentation guidelines. Auto-activate when the user discusses comments, documentation, docstrings, code clarity, API docs, JSDoc, or asks about commenting strategies. |
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The comment would become outdated quickly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
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 Outdated Comments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 $10k, 20% above
This matches IRS publication 501 for 2024
def calculate_progressive_tax(income):
if income <= 10000:
return income * 0.10
else:
return 1000 + (income - 10000) * 0.20
✅ Non-obvious Algorithms
Using Floyd-Warshall for all-pairs shortest paths
because we need distances between all nodes.
Time: O(n³), Space: O(n²)
for k in range(vertices):
for i in range(vertices):
for j in range(vertices):
dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j])
✅ Regex Patterns
Allows letters, numbers, dots, hyphens in username
Requires valid domain and 2+ char extension
email_pattern = r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+.[a-zA-Z]{2,}$'
✅ 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
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 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:
Clear code - Self-explanatory through naming and structure
Good comments - Explain WHY when necessary
Documentation - API docs, docstrings for public interfaces
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.
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
