Agent skill
inline-documentation
Use when writing code - ensure complete JSDoc, docstrings, and inline comments assuming documentation will be generated from code
Install this agent skill to your Project
npx add-skill https://github.com/troykelly/codex-skills/tree/main/skills/inline-documentation
SKILL.md
Inline Documentation
Overview
Document code assuming docs will be generated from it.
Core principle: Future developers (including you) will read this code. Help them.
Announce at use: "I'm adding complete inline documentation for this code."
What to Document
Always Document
| Element | Documentation Required |
|---|---|
| Public functions/methods | Full JSDoc/docstring |
| Public classes | Class-level documentation |
| Public interfaces/types | Description of purpose |
| Exported constants | What they control |
| Complex logic | Why, not what |
| Non-obvious decisions | Explain reasoning |
Skip Documentation For
| Element | Why |
|---|---|
| Private trivial helpers | Self-evident |
| Single-line getters | Obvious from name |
| Standard patterns | Well-known idioms |
| Test files | Tests are documentation |
TypeScript/JavaScript (JSDoc)
Function Documentation
/**
* Calculates the total price including tax and discounts.
*
* @description Applies discounts before tax calculation.
* Discounts are applied in order of magnitude (largest first).
*
* @param items - Line items to calculate
* @param taxRate - Tax rate as decimal (e.g., 0.08 for 8%)
* @param discounts - Optional discount codes to apply
* @returns Total price after discounts and tax
*
* @throws {ValidationError} If taxRate is negative
* @throws {InvalidDiscountError} If discount code is invalid
*
* @example
* ```typescript
* const total = calculateTotal(
* [{ price: 100 }, { price: 50 }],
* 0.08,
* ['SAVE10']
* );
* // Returns: 145.80 (150 - 10% discount = 135, + 8% tax)
* ```
*/
function calculateTotal(
items: LineItem[],
taxRate: number,
discounts?: string[]
): number {
// Implementation
}
Class Documentation
/**
* Manages user authentication and session lifecycle.
*
* @description Handles login, logout, session refresh, and
* multi-device session management. Uses JWT for stateless
* authentication with Redis for session invalidation tracking.
*
* @example
* ```typescript
* const auth = new AuthService(config);
* const session = await auth.login(credentials);
* await auth.logout(session.id);
* ```
*/
class AuthService {
/**
* Creates an AuthService instance.
*
* @param config - Authentication configuration
* @param config.jwtSecret - Secret for signing JWTs
* @param config.sessionTtl - Session time-to-live in seconds
*/
constructor(private config: AuthConfig) { }
/**
* Authenticates a user and creates a session.
*
* @param credentials - User credentials
* @returns Session object with tokens
* @throws {InvalidCredentialsError} If authentication fails
*/
async login(credentials: Credentials): Promise<Session> { }
}
Interface Documentation
/**
* Configuration for the caching layer.
*
* @description Controls cache behavior including TTL,
* invalidation strategy, and storage backend selection.
*/
interface CacheConfig {
/** Time-to-live in seconds. Default: 3600 */
ttl: number;
/** Maximum items to cache. Default: 1000 */
maxSize: number;
/**
* Storage backend to use.
* - 'memory': In-process LRU cache
* - 'redis': Distributed Redis cache
*/
backend: 'memory' | 'redis';
/** Redis connection string (required if backend is 'redis') */
redisUrl?: string;
}
Python (Docstrings)
Function Documentation
def calculate_total(
items: list[LineItem],
tax_rate: float,
discounts: list[str] | None = None
) -> float:
"""Calculate the total price including tax and discounts.
Applies discounts before tax calculation. Discounts are applied
in order of magnitude (largest first).
Args:
items: Line items to calculate.
tax_rate: Tax rate as decimal (e.g., 0.08 for 8%).
discounts: Optional discount codes to apply.
Returns:
Total price after discounts and tax.
Raises:
ValidationError: If tax_rate is negative.
InvalidDiscountError: If discount code is invalid.
Example:
>>> total = calculate_total(
... [LineItem(price=100), LineItem(price=50)],
... 0.08,
... ['SAVE10']
... )
>>> total
145.80 # 150 - 10% = 135, + 8% tax
"""
pass
Class Documentation
class AuthService:
"""Manages user authentication and session lifecycle.
Handles login, logout, session refresh, and multi-device
session management. Uses JWT for stateless authentication
with Redis for session invalidation tracking.
Attributes:
config: Authentication configuration.
redis: Redis client for session tracking.
Example:
>>> auth = AuthService(config)
>>> session = await auth.login(credentials)
>>> await auth.logout(session.id)
"""
def __init__(self, config: AuthConfig) -> None:
"""Create an AuthService instance.
Args:
config: Authentication configuration including
JWT secret and session TTL.
"""
pass
Inline Comments
When to Use
// Complex algorithms
function dijkstra(graph: Graph, start: Node): Map<Node, number> {
// Use priority queue for O(E log V) complexity
// instead of linear search O(V²)
const queue = new PriorityQueue<Node>();
// Initialize all distances to infinity except start
const distances = new Map<Node, number>();
// ... implementation with strategic comments
}
Explain Why, Not What
// BAD: Explains what (obvious from code)
// Increment counter by 1
counter++;
// GOOD: Explains why (not obvious)
// Retry count starts at 1 because initial attempt doesn't count
counter++;
Link to Context
// Per RFC 7519, JWT expiry is in seconds since epoch
const exp = Math.floor(Date.now() / 1000) + ttlSeconds;
// See issue #234 for why we can't use the simpler approach
const result = complexWorkaround();
Mark Non-Obvious Behavior
// IMPORTANT: Order matters here - auth must run before rate limit
app.use(authMiddleware);
app.use(rateLimitMiddleware);
// WARNING: This modifies the input array in place
items.sort((a, b) => a.priority - b.priority);
Documentation Checklist
For each public element:
Functions/Methods
- Brief description (first line)
- Detailed description (if complex)
- All parameters documented
- Return value documented
- Exceptions documented
- Example provided (if non-obvious usage)
Classes
- Class purpose described
- Usage example provided
- All public methods documented
- Public properties documented
Interfaces/Types
- Purpose described
- Each property documented
- Valid values noted (for enums/unions)
Anti-Patterns
| Anti-Pattern | Correct Approach |
|---|---|
| No documentation | Document all public APIs |
| Stale documentation | Update docs with code changes |
| Obvious comments | Only document non-obvious |
| Missing examples | Add examples for complex APIs |
| Copy-paste docs | Write specific documentation |
Generating Documentation
TypeScript
# Using TypeDoc
npx typedoc src/index.ts --out docs
# Using TSDoc
npx @microsoft/api-extractor run
Python
# Using Sphinx
sphinx-apidoc -o docs/source src/
sphinx-build docs/source docs/build
# Using pdoc
pdoc --html src/ -o docs/
Integration
This skill is applied by:
issue-driven-development- Step 7comprehensive-review- Documentation criterion
This skill ensures:
- Maintainable code
- Onboarding ease
- Generated documentation quality
- API discoverability
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