clean-code

Hallucination Traps (Read First)

• ❌ Over-abstracting code that is used in only one place -> ✅ Don't DRY single-use code; premature abstraction is worse than duplication
• ❌ Adding comments that restate what the code does -> ✅ Comments explain WHY, not WHAT; the code explains what
• ❌ Creating utility functions for trivial one-liners -> ✅ Inline is clearer when the operation is self-documenting

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Clean Code — The Art of Readable Software

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Naming

Variables & Functions

// ❌ BAD: Cryptic, abbreviated, meaningless
const d = new Date();
const u = getU();
const flag = true;
function proc(x: number): number {
  return x * 1.08;
}

// ✅ GOOD: Self-documenting, reveals intent
const registrationDate = new Date();
const currentUser = getCurrentUser();
const isEligibleForDiscount = true;
function addSalesTax(price: number): number {
  return price * 1.08;
}

Booleans

// ❌ BAD                    ✅ GOOD
const active = true;
const isActive = true;
const admin = false;
const hasAdminRole = false;
const loading = true;
const isLoading = true;
const open = false;
const isModalOpen = false;
const valid = true;
const canSubmit = true;

// Boolean function names start with is/has/can/should
function isExpired(token: Token): boolean {}
function hasPermission(user: User, action: string): boolean {}
function canRetry(attempt: number): boolean {}
function shouldNotify(event: Event): boolean {}

Constants & Enums

// ❌ BAD: Magic numbers and strings
if (user.role === 3) { ... }
if (retries > 5) { ... }
const delay = 86400000;

// ✅ GOOD: Named constants with meaning
const MAX_RETRY_ATTEMPTS = 5;
const ONE_DAY_MS = 24 * 60 * 60 * 1000;

enum UserRole {
  VIEWER = "viewer",
  EDITOR = "editor",
  ADMIN = "admin",
}

if (user.role === UserRole.ADMIN) { ... }
if (retries > MAX_RETRY_ATTEMPTS) { ... }

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Function Design

Small, Single-Purpose Functions

// ❌ BAD: Does 5 things in one function
async function processOrder(order: Order) {
  // validate
  if (!order.items.length) throw new Error("Empty");
  if (order.total < 0) throw new Error("Negative");
  // calculate
  const subtotal = order.items.reduce((sum, i) => sum + i.price * i.qty, 0);
  const tax = subtotal * 0.08;
  const total = subtotal + tax;
  // save
  await db.orders.insert({ ...order, total });
  // notify
  await emailService.send(order.userId, "Order placed");
  // log
  logger.info("Order processed", { orderId: order.id });
}

// ✅ GOOD: Each function does one thing
async function processOrder(order: Order): Promise<ProcessedOrder> {
  validateOrder(order);
  const totals = calculateTotals(order.items);
  const savedOrder = await saveOrder(order, totals);
  await notifyCustomer(savedOrder);
  return savedOrder;
}

function validateOrder(order: Order): void {
  if (!order.items.length) throw new ValidationError("Order cannot be empty");
  if (order.total < 0) throw new ValidationError("Total cannot be negative");
}

function calculateTotals(items: OrderItem[]): OrderTotals {
  const subtotal = items.reduce((sum, item) => sum + item.price * item.quantity, 0);
  const tax = subtotal * TAX_RATE;
  return { subtotal, tax, total: subtotal + tax };
}

Parameter Rules

// ❌ BAD: Too many parameters
function createUser(
  name: string, email: string, role: string,
  isActive: boolean, avatar: string, bio: string
) { ... }

// ✅ GOOD: Use an object for 3+ parameters
interface CreateUserInput {
  name: string;
  email: string;
  role?: UserRole;
  isActive?: boolean;
  avatar?: string;
  bio?: string;
}

function createUser(input: CreateUserInput): User { ... }

// ❌ BAD: Boolean parameter (caller can't read intent)
setVisible(true);

// ✅ GOOD: Named method instead
show();
hide();

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SOLID Principles (With Code)

S — Single Responsibility

// ❌ BAD: UserService does everything
class UserService {
  createUser() { ... }
  sendEmail() { ... }
  generateReport() { ... }
  uploadAvatar() { ... }
}

// ✅ GOOD: Separate concerns
class UserService { createUser() { ... } }
class EmailService { sendWelcomeEmail() { ... } }
class ReportService { generateUserReport() { ... } }
class AvatarService { upload() { ... } }

O — Open/Closed

// ❌ BAD: Adding a new type requires modifying existing code
function calculateDiscount(type: string, amount: number): number {
  if (type === "student") return amount * 0.2;
  if (type === "veteran") return amount * 0.15;
  if (type === "senior") return amount * 0.1; // must modify for every new type
  return 0;
}

// ✅ GOOD: Open for extension, closed for modification
interface DiscountStrategy {
  calculate(amount: number): number;
}

class StudentDiscount implements DiscountStrategy {
  calculate(amount: number) {
    return amount * 0.2;
  }
}

class VeteranDiscount implements DiscountStrategy {
  calculate(amount: number) {
    return amount * 0.15;
  }
}

// New types = new class, no existing code changes
class EmployeeDiscount implements DiscountStrategy {
  calculate(amount: number) {
    return amount * 0.25;
  }
}

D — Dependency Inversion

// ❌ BAD: High-level module depends on low-level concrete
class OrderService {
  private db = new MySQLDatabase(); // coupled to MySQL
  private mailer = new SendGridMailer(); // coupled to SendGrid
}

// ✅ GOOD: Depend on abstractions (interfaces)
interface Database {
  save(data: unknown): Promise<void>;
}
interface Mailer {
  send(to: string, body: string): Promise<void>;
}

class OrderService {
  constructor(
    private db: Database, // can be MySQL, Postgres, in-memory
    private mailer: Mailer, // can be SendGrid, SES, mock
  ) {}
}

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Error Handling

// ❌ BAD: Swallowing errors
try {
  await saveUser(user);
} catch (e) {
  // silence
}

// ❌ BAD: Generic catch-all
try {
  await processPayment(order);
} catch (e) {
  console.log("Something went wrong");
}

// ✅ GOOD: Handle specific errors, propagate unexpected
try {
  await processPayment(order);
} catch (error) {
  if (error instanceof InsufficientFundsError) {
    return { success: false, message: "Insufficient funds" };
  }
  if (error instanceof PaymentGatewayError) {
    logger.warn("Payment gateway unavailable, queuing for retry", { orderId: order.id });
    await retryQueue.add(order);
    return { success: false, message: "Payment processing delayed" };
  }
  throw error; // unexpected error — let it propagate
}

---

Comments

// ❌ BAD: Comments that restate the code
// Increment i by 1
i++;

// Set the user's name
user.name = newName;

// Check if user is active
if (user.isActive) { ... }

// ✅ GOOD: Comments that explain WHY, not WHAT
// Tax exemption expires after 365 days per IRS Publication 334
const isExempt = daysSinceRegistration < 365;

// Using binary search here because the list is pre-sorted and
// can contain 100K+ items. Linear search caused P95 > 2s.
const index = binarySearch(sortedItems, target);

// Retry 3 times because the payment gateway has transient 503s
// during their daily maintenance window (02:00-02:15 UTC)
const result = await withRetry(() => chargeCard(amount), { maxRetries: 3 });

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Code Smells → Refactoring

Smell                    → Refactoring
───────────────────────────────────────
Long function (>30 lines) → Extract method
Deep nesting (>3 levels)  → Early return / guard clauses
Duplicate code            → Extract shared function
Magic numbers             → Named constants
Boolean parameters        → Separate methods or options object
God class (>300 lines)    → Split into focused classes
Feature envy              → Move method to appropriate class
Primitive obsession       → Value objects (Email, Money, UserId)
Long parameter list       → Parameter object

// Deep nesting → Early return
// ❌ BAD
function processUser(user: User) {
  if (user) {
    if (user.isActive) {
      if (user.hasPermission("edit")) {
        // actual logic buried 3 levels deep
        doStuff();
      }
    }
  }
}

// ✅ GOOD: Guard clauses — fail fast, keep happy path unindented
function processUser(user: User) {
  if (!user) return;
  if (!user.isActive) return;
  if (!user.hasPermission("edit")) return;

  doStuff(); // happy path at top level
}

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AI coding assistants often fall into specific bad habits when dealing with this domain. These are strictly forbidden:

1. Over-engineering: Proposing complex abstractions or distributed systems when a simpler approach suffices.
2. Hallucinated Libraries/Methods: Using non-existent methods or packages. Always // VERIFY or check package.json / requirements.txt.
3. Skipping Edge Cases: Writing the "happy path" and ignoring error handling, timeouts, or data validation.
4. Context Amnesia: Forgetting the user's constraints and offering generic advice instead of tailored solutions.
5. Silent Degradation: Catching and suppressing errors without logging or re-raising.

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Slash command: /review or /tribunal-full Active reviewers: logic-reviewer · security-auditor

❌ Forbidden AI Tropes

1. Blind Assumptions: Never make an assumption without documenting it clearly with // VERIFY: [reason].
2. Silent Degradation: Catching and suppressing errors without logging or handling.
3. Context Amnesia: Forgetting the user's constraints and offering generic advice instead of tailored solutions.

Review these questions before confirming output:

✅ Did I rely ONLY on real, verified tools and methods?
✅ Is this solution appropriately scoped to the user's constraints?
✅ Did I handle potential failure modes and edge cases?
✅ Have I avoided generic boilerplate that doesn't add value?

🛑 Verification-Before-Completion (VBC) Protocol

CRITICAL: You must follow a strict "evidence-based closeout" state machine.

• ❌ Forbidden: Declaring a task complete because the output "looks correct."
• ✅ Required: You are explicitly forbidden from finalizing any task without providing concrete evidence (terminal output, passing tests, compile success, or equivalent proof) that your output works as intended.

Pre-Flight Checklist

• Have I reviewed the user's specific constraints and requests?
• Have I checked the environment for relevant existing implementations?

VBC Protocol (Verification-Before-Completion)

You MUST verify existing code signatures and variables before attempting to modify or call them. No hallucination is permitted.

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🤖 LLM-Specific Traps

AI coding assistants often fall into specific bad habits when dealing with this domain. These are strictly forbidden:

1. Over-engineering: Proposing complex abstractions or distributed systems when a simpler approach suffices.
2. Hallucinated Libraries/Methods: Using non-existent methods or packages. Always // VERIFY or check package.json / requirements.txt.
3. Skipping Edge Cases: Writing the "happy path" and ignoring error handling, timeouts, or data validation.
4. Context Amnesia: Forgetting the user's constraints and offering generic advice instead of tailored solutions.
5. Silent Degradation: Catching and suppressing errors without logging or re-raising.

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🏛️ Tribunal Integration (Anti-Hallucination)

Slash command: /review or /tribunal-full Active reviewers: logic-reviewer · security-auditor

❌ Forbidden AI Tropes

1. Blind Assumptions: Never make an assumption without documenting it clearly with // VERIFY: [reason].
2. Silent Degradation: Catching and suppressing errors without logging or handling.
3. Context Amnesia: Forgetting the user's constraints and offering generic advice instead of tailored solutions.

✅ Pre-Flight Self-Audit

Review these questions before confirming output:

✅ Did I rely ONLY on real, verified tools and methods?
✅ Is this solution appropriately scoped to the user's constraints?
✅ Did I handle potential failure modes and edge cases?
✅ Have I avoided generic boilerplate that doesn't add value?

🛑 Verification-Before-Completion (VBC) Protocol

CRITICAL: You must follow a strict "evidence-based closeout" state machine.

• ❌ Forbidden: Declaring a task complete because the output "looks correct."
• ✅ Required: You are explicitly forbidden from finalizing any task without providing concrete evidence (terminal output, passing tests, compile success, or equivalent proof) that your output works as intended.