TodoWrite Pattern Expert

Incremental Development with Placeholders

Pattern: TodoWrite → Implement → Replace
Tools: TodoWrite tool, TODO comments

Overview

Strategy for breaking complex tasks into manageable pieces using placeholders.

Core Concept

Instead of implementing everything at once:

1. Plan: Identify components needed
2. Scaffold: Create structure with TodoWrite placeholders
3. Implement: Fill in placeholders incrementally
4. Validate: Ensure completeness

Usage Pattern

1. Initial Scaffolding

Example: Building an API:

# Step 1: Create structure with placeholders
class UserAPI:
    def __init__(self):
        TodoWrite("Initialize database connection")

    def create_user(self, email: str, password: str):
        TodoWrite("Validate input")
        TodoWrite("Hash password")
        TodoWrite("Save to database")
        TodoWrite("Return user object")

    def get_user(self, user_id: int):
        TodoWrite("Query database")
        TodoWrite("Handle user not found")

2. Incremental Implementation

Round 1: Critical Path:

def create_user(self, email: str, password: str):
    # ✅ Implemented
    if not email or not password:
        raise ValueError("Email and password required")

    TodoWrite("Hash password")  # Still placeholder
    TodoWrite("Save to database")
    TodoWrite("Return user object")

Round 2: Security:

def create_user(self, email: str, password: str):
    if not email or not password:
        raise ValueError("Email and password required")

    # ✅ Implemented
    import bcrypt
    hashed = bcrypt.hashpw(password.encode(), bcrypt.gensalt())

    TodoWrite("Save to database")
    TodoWrite("Return user object")

3. Completion Validation

Check for remaining TODOs:

# Find all TodoWrite calls
grep -r "TodoWrite" src/

# Or use tool
rg "TodoWrite" --type python

Best Practices

1. Descriptive Placeholders: "TodoWrite('Validate email format')" not "TodoWrite('TODO')".
2. Logical Grouping: Group related TODOs.
3. Priority Order: Implement critical paths first.
4. Track Progress: Maintain list of remaining TODOs.

When to Use TodoWrite

• Complex feature with clear structure
• Uncertain implementation details
• Team collaboration (assign TODO owners)
• Incremental delivery (MVP → full feature)

When NOT to Use

• Simple functions (<20 lines)
• Critical security code (implement immediately)
• One-time scripts

Example: Complete Flow

# Initial (90% TodoWrite)
class PaymentProcessor:
    def process_payment(self, amount, card):
        TodoWrite("Validate amount")
        TodoWrite("Validate card")
        TodoWrite("Call payment gateway")
        TodoWrite("Handle success")
        TodoWrite("Handle failure")
        TodoWrite("Log transaction")

# After Round 1 (50% done)
class PaymentProcessor:
    def process_payment(self, amount, card):
        # ✅ Done
        if amount <= 0:
            raise ValueError("Invalid amount")

        # ✅ Done
        if not card.validate():
            raise ValueError("Invalid card")

        TodoWrite("Call payment gateway")
        TodoWrite("Handle success")
        TodoWrite("Handle failure")
        TodoWrite("Log transaction")

# Final (100% done)
class PaymentProcessor:
    def process_payment(self, amount, card):
        if amount <=  0:
            raise ValueError("Invalid amount")

        if not card.validate():
            raise ValueError("Invalid card")

        # ✅ All implemented
        result = self.gateway.charge(amount, card)

        if result.success:
            self.logger.info(f"Payment success: {result.id}")
            return result
        else:
            self.logger.error(f"Payment failed: {result.error}")
            raise PaymentError(result.error)

Validation Checklist

• Placeholders: Descriptive TodoWrite messages?
• Priority: Critical paths implemented first?
• Tracking: Remaining TODOs documented?
• Completion: All TODOs resolved before merge?

Related Skills

• moai-core-rules: Development workflow
• moai-foundation-specs: Requirement breakdown

Last Updated: 2025-11-20