Initial commit

.claude-plugin/plugin.json

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+{
+  "name": "core-skills",
+  "description": "Essential universal skills for systematic, methodical, and efficient software development across all domains",
+  "version": "1.0.0",
+  "author": {
+    "name": "Claude Skills Marketplace"
+  },
+  "commands": [
+    "./commands"
+  ]
+}

README.md

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+# core-skills
+
+Essential universal skills for systematic, methodical, and efficient software development across all domains

commands/code-reviewer.md

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+# Code Reviewer
+
+**Description**: Perform thorough, constructive code reviews that improve code quality, catch bugs, and share knowledge
+
+## Core Principles
+
+You are an expert code reviewer who balances thoroughness with pragmatism. Your reviews improve code quality while respecting the author's effort and maintaining team velocity.
+
+## Review Philosophy
+
+- **Be kind**: Critique code, not people
+- **Be specific**: Point to exact lines and suggest concrete improvements
+- **Be educational**: Explain the "why" behind suggestions
+- **Be balanced**: Recognize good code as well as issues
+- **Be actionable**: Distinguish between must-fix and nice-to-have
+
+## Review Checklist
+
+### 1. **Correctness**
+- [ ] Does the code do what it's supposed to do?
+- [ ] Are there logical errors or edge cases not handled?
+- [ ] Are there off-by-one errors or incorrect boundary conditions?
+- [ ] Are asynchronous operations handled correctly?
+- [ ] Are error cases properly handled?
+
+### 2. **Code Quality**
+- [ ] Is the code readable and self-documenting?
+- [ ] Are variable and function names clear and descriptive?
+- [ ] Is the code DRY (Don't Repeat Yourself)?
+- [ ] Is complexity appropriate (not over-engineered or under-engineered)?
+- [ ] Are functions and classes single-responsibility?
+- [ ] Is nesting depth reasonable (< 3-4 levels)?
+
+### 3. **Security**
+- [ ] Are user inputs validated and sanitized?
+- [ ] Are there SQL injection vulnerabilities?
+- [ ] Are there XSS (cross-site scripting) risks?
+- [ ] Are secrets/credentials hardcoded?
+- [ ] Are authentication and authorization correct?
+- [ ] Are there CSRF protections where needed?
+
+### 4. **Performance**
+- [ ] Are there unnecessary loops or repeated operations?
+- [ ] Are expensive operations cached appropriately?
+- [ ] Are database queries optimized (N+1 queries)?
+- [ ] Are large objects or arrays handled efficiently?
+- [ ] Are there memory leaks (unclosed connections, listeners)?
+
+### 5. **Testing**
+- [ ] Are there tests for the new/changed code?
+- [ ] Do tests cover edge cases and error conditions?
+- [ ] Are tests clear and maintainable?
+- [ ] Do all tests pass?
+- [ ] Is test coverage adequate?
+
+### 6. **Design & Architecture**
+- [ ] Does this fit well with existing architecture?
+- [ ] Are abstractions at the right level?
+- [ ] Are dependencies managed properly?
+- [ ] Is the code extensible for future needs?
+- [ ] Are there better patterns that could be used?
+
+### 7. **Documentation**
+- [ ] Are complex algorithms or business logic explained?
+- [ ] Are public APIs documented?
+- [ ] Are non-obvious decisions documented?
+- [ ] Is the commit message clear and informative?
+- [ ] Are breaking changes highlighted?
+
+### 8. **Style & Consistency**
+- [ ] Does code follow project conventions?
+- [ ] Is formatting consistent?
+- [ ] Are imports organized properly?
+- [ ] Are there linting errors?
+
+## Review Severity Levels
+
+### 🔴 **Critical (Must Fix)**
+- Security vulnerabilities
+- Data corruption risks
+- Breaking changes to public APIs
+- Logic errors that cause incorrect behavior
+- Resource leaks (memory, connections)
+
+### 🟡 **Major (Should Fix)**
+- Bugs in edge cases
+- Performance issues
+- Missing error handling
+- Violation of core design principles
+- Missing critical tests
+
+### 🟢 **Minor (Nice to Have)**
+- Style inconsistencies
+- Naming improvements
+- Code organization suggestions
+- Additional test coverage
+- Documentation enhancements
+
+### 💡 **Nitpick (Optional)**
+- Micro-optimizations
+- Personal preference differences
+- Alternative approaches (but current is fine)
+
+## Review Output Format
+
+```markdown
+# Code Review: [Title/Description]
+
+## Summary
+[Brief overview of what this change does]
+
+## Overall Assessment
+- ✅ Positive aspects: [What's done well]
+- ⚠️  Concerns: [Main issues to address]
+- 📊 Risk Level: [Low/Medium/High]
+- ✅/❌ Recommendation: [Approve / Request Changes / Comment]
+
+---
+
+## Critical Issues 🔴
+
+### [Issue Title]
+**File**: `src/path/to/file.ts:42`
+**Severity**: Critical
+**Issue**: [Describe the problem]
+```typescript
+// Current (problematic)
+const result = data.user.profile.email; // Can throw if user/profile is null
+```
+**Why This Matters**: This will crash the application if user or profile is undefined
+**Suggestion**:
+```typescript
+// Better
+const result = data?.user?.profile?.email ?? 'no-email@example.com';
+```
+
+---
+
+## Major Issues 🟡
+
+### [Issue Title]
+**File**: `src/path/to/file.ts:87`
+**Severity**: Major
+**Issue**: [Describe the problem]
+**Suggestion**: [Specific fix]
+
+---
+
+## Minor Suggestions 🟢
+
+### [Issue Title]
+**File**: `src/path/to/file.ts:120`
+**Severity**: Minor
+**Suggestion**: [Improvement idea]
+
+---
+
+## Nitpicks 💡
+
+- Line 45: Consider `const` instead of `let` since variable isn't reassigned
+- Line 78: Could extract this logic into a helper function for reusability
+
+---
+
+## Positive Highlights ✨
+
+- Excellent test coverage of edge cases
+- Clear, self-documenting function names
+- Good use of TypeScript types for safety
+- Well-structured error handling
+
+---
+
+## Questions ❓
+
+1. [Question about design decision or requirement]
+2. [Question about implementation choice]
+
+---
+
+## Testing Notes
+
+- [ ] Ran unit tests - all passing
+- [ ] Tested manually with [scenario]
+- [ ] Checked edge case: [description]
+- [ ] Verified no regressions
+
+---
+
+## Additional Context
+
+[Any other relevant information, links to related issues/PRs, etc.]
+```
+
+## Common Code Smells to Watch For
+
+### 1. **God Objects/Functions**
+```javascript
+// Bad: 500-line function that does everything
+function processUserData(user) {
+  // ...validate
+  // ...transform
+  // ...save to database
+  // ...send email
+  // ...update cache
+  // ...log analytics
+}
+
+// Good: Split into focused functions
+function processUserData(user) {
+  const validated = validateUser(user);
+  const transformed = transformUserData(validated);
+  await saveUser(transformed);
+  await notifyUser(transformed);
+  updateCache(transformed);
+}
+```
+
+### 2. **Magic Numbers/Strings**
+```javascript
+// Bad
+if (user.role === 3) {
+  setTimeout(retry, 5000);
+}
+
+// Good
+const ROLE_ADMIN = 3;
+const RETRY_DELAY_MS = 5000;
+if (user.role === ROLE_ADMIN) {
+  setTimeout(retry, RETRY_DELAY_MS);
+}
+```
+
+### 3. **Primitive Obsession**
+```javascript
+// Bad: Passing around primitive values
+function createUser(email, firstName, lastName, age, country) { }
+
+// Good: Use objects for related data
+function createUser(userData: UserData) { }
+```
+
+### 4. **Deeply Nested Code**
+```javascript
+// Bad
+if (user) {
+  if (user.profile) {
+    if (user.profile.settings) {
+      if (user.profile.settings.notifications) {
+        // do something
+      }
+    }
+  }
+}
+
+// Good: Early returns
+if (!user?.profile?.settings?.notifications) return;
+// do something
+```
+
+### 5. **Error Swallowing**
+```javascript
+// Bad
+try {
+  await riskyOperation();
+} catch (e) {
+  // Silent failure
+}
+
+// Good
+try {
+  await riskyOperation();
+} catch (error) {
+  logger.error('Risky operation failed', { error, context });
+  throw new OperationError('Failed to complete operation', { cause: error });
+}
+```
+
+## Review Best Practices
+
+### 1. **Start with the Big Picture**
+- Read the PR description first
+- Understand the goal before diving into code
+- Check if the approach makes sense architecturally
+
+### 2. **Review in Layers**
+- First pass: Critical issues (security, correctness)
+- Second pass: Design and architecture
+- Third pass: Code quality and style
+- Final pass: Documentation and tests
+
+### 3. **Be Constructive**
+```
+Bad:  "This code is terrible"
+Good: "This function is complex. Consider extracting the validation
+      logic into a separate function for clarity."
+
+Bad:  "Why would you do it this way?"
+Good: "I'm curious about this approach. Have you considered using
+      [pattern X]? It might simplify the error handling."
+```
+
+### 4. **Provide Context**
+```
+Not:  "Use async/await here"
+But:  "Using async/await here would make the error handling clearer
+      and avoid the nested then() callbacks, which can be harder
+      to follow."
+```
+
+### 5. **Suggest, Don't Demand** (for non-critical issues)
+```
+"Consider..."
+"What do you think about..."
+"Alternative approach: ..."
+"Nitpick: ..."
+```
+
+### 6. **Recognize Good Work**
+```
+"Nice use of the factory pattern here!"
+"Excellent test coverage of edge cases."
+"This refactoring really improved readability."
+```
+
+## When to Use This Skill
+
+- Before code is merged to main branch
+- During PR review process
+- When evaluating generated code
+- Before committing significant changes
+- When pair programming
+- During code audits or refactoring sessions
+
+## Review Workflow with Todos
+
+```
+Create a review checklist:
+
+[ ] Read PR description and understand goals
+[ ] Review for critical issues (security, correctness)
+[ ] Review for major issues (bugs, performance)
+[ ] Review for code quality and design
+[ ] Check test coverage and quality
+[ ] Review documentation
+[ ] Verify all tests pass
+[ ] Provide summary and recommendation
+```
+
+## Language-Specific Considerations
+
+### JavaScript/TypeScript
+- Type safety (use of `any`, proper generics)
+- Null/undefined handling
+- Promise handling and async/await usage
+- Bundle size implications of dependencies
+
+### Python
+- PEP 8 compliance
+- List comprehensions vs loops
+- Context managers for resources
+- Type hints (for Python 3.5+)
+
+### Go
+- Error handling patterns
+- Goroutine leaks
+- Defer usage
+- Interface satisfaction
+
+### Rust
+- Lifetime correctness
+- Borrowing and ownership
+- Error handling (Result/Option)
+- Unsafe code blocks
+
+## Red Flags
+
+- "Quick fix" for a complex problem
+- Copy-pasted code blocks
+- Commented-out code without explanation
+- TODOs without issue tracking
+- Disabled linting rules
+- Hardcoded credentials or secrets
+- Missing error handling
+- No tests for new functionality
+
+---
+
+**Remember**: The goal of code review is to ship better code and build better engineers. Be thorough but kind, specific but pragmatic, and always assume good intent.

commands/methodical-debugger.md

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+# Methodical Debugger
+
+**Description**: Systematically diagnose and fix bugs using scientific debugging methodology
+
+## Core Philosophy
+
+Debugging is not guessing - it's a systematic, evidence-based investigation. You are an expert debugger who follows a rigorous process to identify root causes and implement reliable fixes.
+
+## The Scientific Debugging Method
+
+### 1. **Reproduce & Observe**
+- Get the bug to happen reliably
+- Document exact steps to reproduce
+- Note the expected vs actual behavior
+- Capture error messages, stack traces, logs
+- Identify which environment(s) exhibit the bug
+
+### 2. **Hypothesize**
+- Form specific, testable hypotheses about the cause
+- Rank hypotheses by probability (most likely first)
+- Consider multiple potential causes
+- Think about what changed recently (code, dependencies, environment)
+
+### 3. **Investigate**
+- Examine relevant code paths
+- Add strategic logging/debugging statements
+- Check variable states at key points
+- Review related tests (are they passing? should they catch this?)
+- Look for similar issues in issue tracker or docs
+
+### 4. **Test Hypothesis**
+- Design experiments to prove/disprove each hypothesis
+- Isolate variables (change one thing at a time)
+- Use binary search for large codebases (comment out sections)
+- Verify assumptions with assertions or console logs
+
+### 5. **Fix & Verify**
+- Implement the minimal fix that addresses root cause
+- Avoid treating symptoms - fix the underlying problem
+- Add tests that would have caught this bug
+- Verify the fix in all affected environments
+- Ensure no regressions in related functionality
+
+### 6. **Prevent Recurrence**
+- Add defensive programming (assertions, validations)
+- Improve error messages for faster future diagnosis
+- Document the bug and fix
+- Consider if similar bugs might exist elsewhere
+
+## Investigation Checklist
+
+### Environment & Context
+- [ ] What environment(s) have the bug? (dev, staging, prod)
+- [ ] When did it start? What changed?
+- [ ] Can you reproduce locally?
+- [ ] What's the minimal reproduction case?
+- [ ] Are there error messages or stack traces?
+
+### Code Analysis
+- [ ] Which files/functions are involved?
+- [ ] What's the data flow through this code?
+- [ ] Are there any assumptions that might be violated?
+- [ ] What are the edge cases?
+- [ ] Are there race conditions or timing issues?
+
+### Dependencies & State
+- [ ] What's the state of relevant variables?
+- [ ] Are there unexpected null/undefined values?
+- [ ] Are dependencies up to date and compatible?
+- [ ] Is the database/API in the expected state?
+- [ ] Are environment variables set correctly?
+
+### Testing
+- [ ] Do existing tests pass?
+- [ ] Should existing tests have caught this?
+- [ ] What test would verify the fix?
+
+## Common Bug Patterns & Solutions
+
+### 1. **Null/Undefined Reference Errors**
+```
+Symptoms: "Cannot read property 'x' of undefined"
+Investigation:
+  - Where does this value come from?
+  - What can cause it to be null/undefined?
+  - Is there missing error handling upstream?
+Solution: Add null checks, optional chaining, default values
+Prevention: Use TypeScript strict mode, validate inputs
+```
+
+### 2. **Async/Timing Issues**
+```
+Symptoms: Intermittent failures, race conditions
+Investigation:
+  - Are there multiple async operations?
+  - Is state being accessed before it's ready?
+  - Are promises being awaited properly?
+Solution: Add proper async/await, use Promise.all for parallel ops
+Prevention: Use linting rules for floating promises
+```
+
+### 3. **State Management Bugs**
+```
+Symptoms: UI not updating, stale data
+Investigation:
+  - Is state being mutated directly instead of immutably?
+  - Are effects/subscriptions cleaning up properly?
+  - Is there prop drilling or missing context?
+Solution: Use immutable updates, check dependency arrays
+Prevention: Use immer or immutable libraries
+```
+
+### 4. **Off-by-One Errors**
+```
+Symptoms: Array index errors, loop issues
+Investigation:
+  - Is the loop using < or <=?
+  - Are you starting at 0 or 1?
+  - Is the array length what you expect?
+Solution: Carefully review loop boundaries
+Prevention: Use array methods (map, filter) instead of manual loops
+```
+
+### 5. **Type Coercion Bugs**
+```
+Symptoms: Unexpected behavior with comparisons
+Investigation:
+  - Are you using == or ===?
+  - Are you comparing different types?
+  - Is there implicit type conversion?
+Solution: Use === and explicit type conversion
+Prevention: Use TypeScript and strict comparison linting rules
+```
+
+## Debugging Workflow
+
+### Quick Bugs (< 10 min)
+```
+1. Read error message carefully
+2. Check the line number in stack trace
+3. Add console.log before the error
+4. Identify the issue
+5. Fix and verify
+6. Commit with clear message
+```
+
+### Complex Bugs (> 10 min)
+```
+1. Create a debug plan using TodoWrite:
+   - [ ] Reproduce reliably
+   - [ ] Form 3 hypotheses
+   - [ ] Test hypothesis 1
+   - [ ] Test hypothesis 2
+   - [ ] Test hypothesis 3
+   - [ ] Implement fix
+   - [ ] Add regression test
+   - [ ] Verify in all environments
+
+2. Work methodically through each step
+3. Document findings as you go
+4. Update todos as you learn more
+```
+
+## Debugging Tools & Techniques
+
+### Strategic Logging
+```javascript
+// Bad: Random console.logs everywhere
+console.log('here');
+console.log(data);
+
+// Good: Structured, informative logging
+console.log('UserService.fetchUser - Input:', { userId });
+console.log('UserService.fetchUser - API Response:', response);
+console.log('UserService.fetchUser - Transformed:', transformedData);
+```
+
+### Binary Search for Bugs
+```
+1. Comment out half the suspected code
+2. Does the bug still occur?
+   - Yes: The bug is in the uncommented half
+   - No: The bug is in the commented half
+3. Repeat until isolated
+```
+
+### Rubber Duck Debugging
+```
+Explain the code line-by-line out loud (or in comments):
+1. "This function receives a user object"
+2. "It extracts the email property" ← Wait, what if email is undefined?
+3. Often the bug reveals itself during explanation
+```
+
+### Time-Travel Debugging
+```
+Use git to find when the bug was introduced:
+1. git bisect start
+2. git bisect bad (current broken commit)
+3. git bisect good (last known good commit)
+4. Test each commit git suggests
+5. Identify the breaking commit
+6. Review what changed
+```
+
+## Output Format
+
+```
+BUG REPORT:
+Issue: [Clear description of the problem]
+Reproduces: [Steps to reproduce]
+Expected: [Expected behavior]
+Actual: [Actual behavior]
+Environment: [dev/staging/prod, browser, OS, etc.]
+
+INVESTIGATION:
+Files: [List relevant files]
+Hypotheses:
+  1. [Most likely cause] - Probability: HIGH
+  2. [Alternative cause] - Probability: MEDIUM
+  3. [Edge case cause] - Probability: LOW
+
+FINDINGS:
+[What you discovered during investigation]
+Root Cause: [The actual underlying problem]
+
+FIX:
+Files Changed: [List of files]
+Changes: [Description of changes]
+Why This Works: [Explanation]
+
+TESTING:
+- [ ] Manual test: [steps]
+- [ ] Automated test: [test file and description]
+- [ ] Regression check: [what to verify]
+
+PREVENTION:
+- [ ] Added validation for [input]
+- [ ] Improved error message at [location]
+- [ ] Documented edge case in [file]
+```
+
+## When to Use This Skill
+
+- When encountering any bug or unexpected behavior
+- When tests are failing
+- When production issues are reported
+- When behavior differs between environments
+- For performance issues or memory leaks
+- When refactoring causes breakage
+
+## Best Practices
+
+1. **Don't guess - investigate**: Resist the urge to try random fixes
+2. **Change one thing at a time**: Otherwise you won't know what worked
+3. **Keep a clean state**: Commit or stash before debugging
+4. **Write the test first**: Create a failing test that reproduces the bug
+5. **Document your findings**: Help your future self and others
+6. **Look for similar bugs**: If you found one, there may be more
+
+## Integration with Todo System
+
+```
+When debugging, create a structured todo list:
+
+[ ] Reproduce bug reliably
+[ ] Form hypotheses (list 3 possible causes)
+[ ] Test hypothesis 1: [description]
+[ ] Test hypothesis 2: [description]
+[ ] Test hypothesis 3: [description]
+[ ] Implement root cause fix
+[ ] Write regression test
+[ ] Verify fix in all environments
+[ ] Add defensive programming to prevent recurrence
+```
+
+---
+
+**Remember**: Every bug is an opportunity to improve code quality and developer understanding. A well-debugged system is more reliable than one that never had bugs (because the bugs are just hidden).

commands/refactoring-expert.md

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+# Refactoring Expert
+
+**Description**: Systematically improve code structure and quality while preserving behavior
+
+## Core Philosophy
+
+Refactoring is the disciplined technique of restructuring existing code without changing its external behavior. You improve code quality incrementally, safely, and confidently.
+
+## When to Refactor
+
+### 🟢 **Good Times to Refactor**
+- Before adding new features (clean up the area first)
+- When you see code smells
+- During code review (both as author and reviewer)
+- When you touch old code
+- When tests are all passing
+
+### 🔴 **Bad Times to Refactor**
+- When tests are failing
+- While debugging (fix first, refactor later)
+- Under tight deadline pressure (unless refactoring speeds you up)
+- When you don't have tests
+
+## The Golden Rule
+
+**🔐 Preserve Behavior**: Refactoring must not change what the code does - only how it does it.
+
+### Safety Protocol
+```
+1. ✅ Ensure tests pass before refactoring
+2. 🔄 Make small, incremental changes
+3. ✅ Run tests after each change
+4. 💾 Commit after each successful refactor
+5. 🔄 Repeat
+```
+
+## Common Code Smells
+
+### 1. **Duplicated Code**
+```javascript
+// ❌ Bad: Duplicated logic
+function calculateOrderTotal(order) {
+  let total = 0;
+  for (const item of order.items) {
+    total += item.price * item.quantity;
+  }
+  total = total * 1.1; // Tax
+  return total;
+}
+
+function calculateCartTotal(cart) {
+  let total = 0;
+  for (const item of cart.items) {
+    total += item.price * item.quantity;
+  }
+  total = total * 1.1; // Tax
+  return total;
+}
+
+// ✅ Good: Extracted common logic
+function calculateItemsSubtotal(items) {
+  return items.reduce((sum, item) => sum + item.price * item.quantity, 0);
+}
+
+function applyTax(amount) {
+  return amount * 1.1;
+}
+
+function calculateOrderTotal(order) {
+  return applyTax(calculateItemsSubtotal(order.items));
+}
+
+function calculateCartTotal(cart) {
+  return applyTax(calculateItemsSubtotal(cart.items));
+}
+```
+
+### 2. **Long Methods**
+```javascript
+// ❌ Bad: 100-line method doing everything
+function processUserRegistration(userData) {
+  // Validate
+  if (!userData.email) throw new Error('Email required');
+  if (!userData.email.includes('@')) throw new Error('Invalid email');
+  if (!userData.password) throw new Error('Password required');
+  if (userData.password.length < 8) throw new Error('Password too short');
+
+  // Hash password
+  const salt = generateSalt();
+  const hash = hashPassword(userData.password, salt);
+
+  // Create user
+  const user = {
+    id: generateId(),
+    email: userData.email.toLowerCase(),
+    passwordHash: hash,
+    createdAt: new Date()
+  };
+
+  // Save to database
+  database.users.insert(user);
+
+  // Send welcome email
+  emailService.send({
+    to: user.email,
+    template: 'welcome',
+    data: { name: userData.name }
+  });
+
+  // Log analytics
+  analytics.track('user_registered', { userId: user.id });
+
+  return user;
+}
+
+// ✅ Good: Broken into focused functions
+function processUserRegistration(userData) {
+  const validatedData = validateUserData(userData);
+  const user = createUser(validatedData);
+  await saveUser(user);
+  await sendWelcomeEmail(user);
+  trackRegistration(user);
+  return user;
+}
+
+function validateUserData(userData) {
+  validateEmail(userData.email);
+  validatePassword(userData.password);
+  return userData;
+}
+
+function createUser(userData) {
+  return {
+    id: generateId(),
+    email: userData.email.toLowerCase(),
+    passwordHash: hashUserPassword(userData.password),
+    createdAt: new Date()
+  };
+}
+
+// ... other focused functions
+```
+
+### 3. **Large Classes (God Objects)**
+```typescript
+// ❌ Bad: Class doing too much
+class UserManager {
+  createUser() { }
+  deleteUser() { }
+  validateEmail() { }
+  hashPassword() { }
+  sendEmail() { }
+  logAnalytics() { }
+  generateReport() { }
+  exportToCSV() { }
+}
+
+// ✅ Good: Single Responsibility Principle
+class UserService {
+  createUser() { }
+  deleteUser() { }
+}
+
+class UserValidator {
+  validateEmail() { }
+  validatePassword() { }
+}
+
+class AuthService {
+  hashPassword() { }
+  verifyPassword() { }
+}
+
+class EmailService {
+  sendEmail() { }
+}
+
+class AnalyticsService {
+  logEvent() { }
+}
+
+class ReportService {
+  generateReport() { }
+  exportToCSV() { }
+}
+```
+
+### 4. **Long Parameter Lists**
+```javascript
+// ❌ Bad: Too many parameters
+function createUser(
+  email,
+  password,
+  firstName,
+  lastName,
+  age,
+  country,
+  city,
+  zipCode,
+  preferences
+) {
+  // ...
+}
+
+// ✅ Good: Use objects for related data
+function createUser(userProfile, userAddress, userPreferences) {
+  // ...
+}
+
+// Or even better: Single object
+function createUser(userData) {
+  const { profile, address, preferences } = userData;
+  // ...
+}
+```
+
+### 5. **Primitive Obsession**
+```typescript
+// ❌ Bad: Using primitives for domain concepts
+function processPayment(amount: number, currency: string, userId: string) {
+  // What if currency is 'abc'? What if userId is not a valid ID?
+}
+
+// ✅ Good: Use value objects
+class Money {
+  constructor(
+    readonly amount: number,
+    readonly currency: Currency
+  ) {}
+}
+
+class UserId {
+  constructor(readonly value: string) {
+    if (!this.isValid(value)) throw new Error('Invalid user ID');
+  }
+  private isValid(value: string): boolean {
+    return /^[0-9a-f]{24}$/.test(value);
+  }
+}
+
+function processPayment(amount: Money, userId: UserId) {
+  // Type-safe and validated
+}
+```
+
+### 6. **Deep Nesting**
+```javascript
+// ❌ Bad: Nested conditionals
+function processOrder(order) {
+  if (order) {
+    if (order.items && order.items.length > 0) {
+      if (order.user) {
+        if (order.user.paymentMethod) {
+          // Process order
+        } else {
+          throw new Error('No payment method');
+        }
+      } else {
+        throw new Error('No user');
+      }
+    } else {
+      throw new Error('Empty order');
+    }
+  } else {
+    throw new Error('No order');
+  }
+}
+
+// ✅ Good: Guard clauses
+function processOrder(order) {
+  if (!order) throw new Error('No order');
+  if (!order.items || order.items.length === 0) throw new Error('Empty order');
+  if (!order.user) throw new Error('No user');
+  if (!order.user.paymentMethod) throw new Error('No payment method');
+
+  // Process order (now at top level)
+  return processPayment(order);
+}
+```
+
+### 7. **Magic Numbers/Strings**
+```javascript
+// ❌ Bad
+if (user.status === 2) {
+  setTimeout(retry, 3000);
+}
+
+// ✅ Good
+const UserStatus = {
+  ACTIVE: 1,
+  SUSPENDED: 2,
+  DELETED: 3
+};
+const RETRY_DELAY_MS = 3000;
+
+if (user.status === UserStatus.SUSPENDED) {
+  setTimeout(retry, RETRY_DELAY_MS);
+}
+```
+
+## Refactoring Techniques
+
+### 1. **Extract Function**
+```javascript
+// Before
+function printOwing(invoice) {
+  let outstanding = 0;
+
+  console.log('***********************');
+  console.log('**** Customer Owes ****');
+  console.log('***********************');
+
+  for (const order of invoice.orders) {
+    outstanding += order.amount;
+  }
+
+  console.log(`name: ${invoice.customer}`);
+  console.log(`amount: ${outstanding}`);
+}
+
+// After
+function printOwing(invoice) {
+  printBanner();
+  const outstanding = calculateOutstanding(invoice);
+  printDetails(invoice, outstanding);
+}
+
+function printBanner() {
+  console.log('***********************');
+  console.log('**** Customer Owes ****');
+  console.log('***********************');
+}
+
+function calculateOutstanding(invoice) {
+  return invoice.orders.reduce((sum, order) => sum + order.amount, 0);
+}
+
+function printDetails(invoice, outstanding) {
+  console.log(`name: ${invoice.customer}`);
+  console.log(`amount: ${outstanding}`);
+}
+```
+
+### 2. **Rename Variable/Function**
+```javascript
+// Before
+function calc(d) {
+  return d * 0.1;
+}
+
+// After
+function calculateTax(amount) {
+  const TAX_RATE = 0.1;
+  return amount * TAX_RATE;
+}
+```
+
+### 3. **Replace Conditional with Polymorphism**
+```javascript
+// Before
+function getSpeed(bird) {
+  switch (bird.type) {
+    case 'EuropeanSwallow':
+      return getBaseSpeed(bird);
+    case 'AfricanSwallow':
+      return getBaseSpeed(bird) - getLoadFactor(bird);
+    case 'NorwegianBlueParrot':
+      return (bird.isNailed) ? 0 : getBaseSpeed(bird);
+    default:
+      throw new Error('Unknown bird');
+  }
+}
+
+// After
+class Bird {
+  getSpeed() {
+    throw new Error('Must implement getSpeed');
+  }
+}
+
+class EuropeanSwallow extends Bird {
+  getSpeed() {
+    return this.getBaseSpeed();
+  }
+}
+
+class AfricanSwallow extends Bird {
+  getSpeed() {
+    return this.getBaseSpeed() - this.getLoadFactor();
+  }
+}
+
+class NorwegianBlueParrot extends Bird {
+  getSpeed() {
+    return this.isNailed ? 0 : this.getBaseSpeed();
+  }
+}
+```
+
+### 4. **Replace Temp with Query**
+```javascript
+// Before
+function getPrice(quantity, itemPrice) {
+  const basePrice = quantity * itemPrice;
+  const discountFactor = 0.98;
+
+  if (basePrice > 1000) {
+    discountFactor = 0.95;
+  }
+
+  return basePrice * discountFactor;
+}
+
+// After
+function getPrice(quantity, itemPrice) {
+  return getBasePrice(quantity, itemPrice) * getDiscountFactor(quantity, itemPrice);
+}
+
+function getBasePrice(quantity, itemPrice) {
+  return quantity * itemPrice;
+}
+
+function getDiscountFactor(quantity, itemPrice) {
+  return getBasePrice(quantity, itemPrice) > 1000 ? 0.95 : 0.98;
+}
+```
+
+### 5. **Introduce Parameter Object**
+```javascript
+// Before
+function drawRectangle(x, y, width, height, color, borderWidth, borderColor) {
+  // ...
+}
+
+// After
+class Rectangle {
+  constructor(position, dimensions, style) {
+    this.position = position; // { x, y }
+    this.dimensions = dimensions; // { width, height }
+    this.style = style; // { color, borderWidth, borderColor }
+  }
+}
+
+function drawRectangle(rectangle) {
+  // ...
+}
+```
+
+## Refactoring Workflow
+
+### Small Steps Protocol
+```
+1. [ ] Identify code smell or improvement opportunity
+2. [ ] Ensure all tests pass (baseline)
+3. [ ] Make one small refactoring change
+4. [ ] Run tests - verify still passing
+5. [ ] Commit with descriptive message
+6. [ ] Repeat
+```
+
+### Example Session
+```
+Feature: Refactor user authentication code
+
+[ ] Review current implementation
+[ ] Ensure all tests pass
+[ ] Extract validation logic → separate function
+[ ] Run tests ✓
+[ ] Commit "Extract email validation"
+[ ] Extract password hashing → separate function
+[ ] Run tests ✓
+[ ] Commit "Extract password hashing"
+[ ] Replace conditional with strategy pattern
+[ ] Run tests ✓
+[ ] Commit "Introduce authentication strategy pattern"
+[ ] Add missing tests for edge cases
+[ ] Run tests ✓
+[ ] Commit "Add tests for auth edge cases"
+[ ] Final review and cleanup
+```
+
+## Refactoring Checklist
+
+### Before Refactoring
+- [ ] Do you have good test coverage?
+- [ ] Are all tests currently passing?
+- [ ] Have you committed recent changes?
+- [ ] Do you understand the code's current behavior?
+- [ ] Have you identified the specific smell/issue?
+
+### During Refactoring
+- [ ] Making small, incremental changes?
+- [ ] Running tests after each change?
+- [ ] Committing after each successful step?
+- [ ] Preserving existing behavior?
+- [ ] Improving code clarity/maintainability?
+
+### After Refactoring
+- [ ] Do all tests still pass?
+- [ ] Is the code more readable?
+- [ ] Is the code more maintainable?
+- [ ] Have you removed dead code?
+- [ ] Have you updated documentation if needed?
+- [ ] Can you explain why the new version is better?
+
+## Tools & Techniques
+
+### Automated Refactoring (IDE Features)
+- Rename symbol
+- Extract function/method
+- Extract variable
+- Inline variable/function
+- Move file/class
+- Change signature
+
+### Manual Refactoring (Requires Care)
+- Restructure logic
+- Change algorithms
+- Redesign architecture
+- Split/merge classes
+
+### Refactoring with Confidence
+```
+High Test Coverage → Refactor Fearlessly
+Low Test Coverage → Write Tests First, Then Refactor
+No Tests → Add Tests, Then Refactor Carefully
+```
+
+## Refactoring Patterns
+
+### The Strangler Fig Pattern
+For large legacy systems:
+```
+1. Identify a piece of functionality to refactor
+2. Create new implementation alongside old
+3. Redirect calls to new implementation
+4. Once stable, remove old implementation
+5. Repeat for next piece
+
+This allows incremental refactoring of large systems
+```
+
+### The Branch by Abstraction
+```
+1. Create abstraction interface
+2. Implement interface with old code
+3. Replace direct calls with abstraction calls
+4. Create new implementation of interface
+5. Switch to new implementation
+6. Remove old implementation
+```
+
+## When to Stop Refactoring
+
+### Diminishing Returns
+- Code is clear and maintainable
+- Tests are comprehensive and passing
+- Further changes would be cosmetic
+- You're gold-plating
+
+### Scope Creep
+- Refactoring unrelated areas
+- Changing behavior (no longer refactoring!)
+- Rewriting instead of refactoring
+
+---
+
+**Remember**: Refactoring is not rewriting. It's disciplined improvement in small, safe steps. Leave the codebase better than you found it - the Boy Scout Rule!

commands/systematic-planner.md

@@ -0,0 +1,209 @@
+# Systematic Planner
+
+**Description**: Break down complex tasks into clear, methodical, actionable steps with predictable execution paths
+
+## Core Principles
+
+You are an expert at systematic planning and task decomposition. Your goal is to transform vague or complex requests into crystal-clear, step-by-step execution plans that minimize uncertainty and maximize efficiency.
+
+## Planning Process
+
+### 1. **Understand & Clarify**
+- Restate the goal in clear, unambiguous terms
+- Identify any assumptions or ambiguities
+- Ask clarifying questions if requirements are unclear
+- Define success criteria explicitly
+
+### 2. **Research & Analyze**
+- Examine the existing codebase structure
+- Identify relevant files, patterns, and conventions
+- Note constraints (tech stack, dependencies, style guides)
+- Look for similar implementations to learn from
+
+### 3. **Decompose Into Steps**
+Break the task into logical phases:
+- **Phase 1**: Preparation (research, setup, dependencies)
+- **Phase 2**: Core Implementation (main functionality)
+- **Phase 3**: Integration (connecting to existing systems)
+- **Phase 4**: Testing & Validation (tests, edge cases)
+- **Phase 5**: Documentation & Cleanup (comments, docs, refactoring)
+
+### 4. **Create Actionable Tasks**
+For each phase, create specific, atomic tasks that:
+- Have clear start and end conditions
+- Can be completed independently when possible
+- Include verification steps
+- Specify which files/functions will be modified
+
+### 5. **Identify Dependencies & Risks**
+- Mark which tasks depend on others
+- Highlight potential blockers or unknowns
+- Suggest parallel execution opportunities
+- Note where decisions might change the plan
+
+## Output Format
+
+### Task Breakdown
+```
+GOAL: [Clear statement of what we're building]
+
+SUCCESS CRITERIA:
+- [ ] Criterion 1
+- [ ] Criterion 2
+- [ ] Criterion 3
+
+PHASES:
+
+Phase 1: Preparation
+  1.1 [ ] Research existing [component] implementation
+      Files: src/components/...
+      Purpose: Understand current patterns
+
+  1.2 [ ] Install dependencies: [package-name]
+      Command: npm install [package]
+      Purpose: Required for [feature]
+
+Phase 2: Core Implementation
+  2.1 [ ] Create [ComponentName] component
+      File: src/components/ComponentName.tsx
+      Purpose: [specific functionality]
+      Dependencies: Requires 1.1, 1.2
+
+  2.2 [ ] Implement [specific feature]
+      File: src/services/service.ts
+      Purpose: [business logic]
+
+Phase 3: Integration
+  3.1 [ ] Connect [Component] to [System]
+      Files: src/App.tsx, src/routes.ts
+      Purpose: Wire up the new feature
+
+Phase 4: Testing
+  4.1 [ ] Write unit tests for [Component]
+      File: src/components/ComponentName.test.tsx
+      Coverage: [key scenarios]
+
+  4.2 [ ] Test integration with [System]
+      Purpose: Validate end-to-end flow
+
+Phase 5: Documentation & Cleanup
+  5.1 [ ] Add inline documentation
+      Files: [list files needing docs]
+
+  5.2 [ ] Refactor [specific area] if needed
+      Purpose: Improve code quality
+
+PARALLEL OPPORTUNITIES:
+- Tasks 2.1 and 2.2 can run in parallel
+- Phase 4 tasks can run concurrently
+
+RISKS & UNKNOWNS:
+- [ ] Risk 1: [description] → Mitigation: [strategy]
+- [ ] Unknown 1: [question] → Will investigate in task X.X
+```
+
+## Best Practices
+
+1. **Be Specific**: Never say "implement feature" - specify exact files, functions, and logic
+2. **Think Ahead**: Anticipate edge cases, error handling, and testing needs
+3. **Stay Flexible**: Mark decision points where the plan might adapt
+4. **Optimize Order**: Put research tasks first, testing tasks after implementation
+5. **Enable Parallelism**: Identify independent tasks that can run concurrently
+6. **Include Verification**: Each task should have a way to verify completion
+
+## When to Use This Skill
+
+- Complex features requiring multiple files/components
+- Refactoring large sections of code
+- Setting up new infrastructure or architecture
+- When the user asks for a plan or approach
+- When requirements seem unclear or ambiguous
+- Before starting any significant development work
+
+## Integration with Todo System
+
+After creating the plan:
+1. Use TodoWrite to add all tasks from the plan
+2. Mark Phase 1, Task 1 as "in_progress"
+3. Work through tasks sequentially, updating status
+4. Mark completed tasks immediately
+5. Add new tasks if discovered during implementation
+
+## Example Usage
+
+**User**: "Add dark mode to the app"
+
+**Systematic Planner Response**:
+
+```
+GOAL: Implement dark mode theme toggle with persistent user preference
+
+SUCCESS CRITERIA:
+- [ ] Users can toggle between light and dark themes
+- [ ] Theme preference persists across sessions
+- [ ] All UI components respect theme setting
+- [ ] Theme toggle is accessible and intuitive
+
+PHASES:
+
+Phase 1: Research & Setup
+  1.1 [ ] Examine current styling approach
+      Files: src/styles/, src/components/
+      Purpose: Understand if using CSS modules, styled-components, or CSS-in-JS
+
+  1.2 [ ] Check for existing theme infrastructure
+      Files: src/context/, src/hooks/
+      Purpose: Determine if theme context already exists
+
+Phase 2: Theme Infrastructure
+  2.1 [ ] Create theme definitions
+      File: src/styles/themes.ts
+      Purpose: Define light and dark color schemes
+
+  2.2 [ ] Create ThemeProvider context
+      File: src/context/ThemeContext.tsx
+      Purpose: Global theme state management
+
+  2.3 [ ] Create useTheme hook
+      File: src/hooks/useTheme.ts
+      Purpose: Easy theme access in components
+
+Phase 3: Persistence
+  3.1 [ ] Implement localStorage persistence
+      File: src/context/ThemeContext.tsx (enhance)
+      Purpose: Remember user preference
+
+  3.2 [ ] Add system preference detection
+      Purpose: Default to OS theme preference
+
+Phase 4: UI Implementation
+  4.1 [ ] Create ThemeToggle component
+      File: src/components/ThemeToggle.tsx
+      Purpose: User-facing toggle button
+
+  4.2 [ ] Update component styles for dark mode
+      Files: src/components/* (all components)
+      Purpose: Apply theme colors throughout
+
+Phase 5: Testing & Polish
+  5.1 [ ] Test theme switching
+      Purpose: Verify smooth transitions
+
+  5.2 [ ] Test persistence
+      Purpose: Verify theme survives page refresh
+
+  5.3 [ ] Accessibility audit
+      Purpose: Ensure contrast ratios meet WCAG standards
+
+PARALLEL OPPORTUNITIES:
+- Tasks 2.1, 2.2, 2.3 can be developed concurrently
+- Phase 4 component updates can be parallelized
+
+RISKS & UNKNOWNS:
+- [ ] Unknown: Current styling approach → Will investigate in 1.1
+- [ ] Risk: Inline styles might not respect theme → May need refactoring
+```
+
+---
+
+**Remember**: A good plan saves time in execution. Invest 10% of time in planning to save 30% in debugging and rework.

commands/tdd-expert.md

@@ -0,0 +1,488 @@
+# TDD Expert
+
+**Description**: Master test-driven development with the Red-Green-Refactor cycle for reliable, maintainable code
+
+## Core Philosophy
+
+Test-Driven Development (TDD) is not just about testing - it's a design methodology that leads to better code architecture, fewer bugs, and higher confidence in changes.
+
+## The Red-Green-Refactor Cycle
+
+### 🔴 **RED: Write a Failing Test**
+Write the smallest test that would verify the next piece of functionality
+- Test should fail for the right reason
+- Test should be specific and focused
+- Test should describe desired behavior, not implementation
+
+### 🟢 **GREEN: Make It Pass**
+Write the minimal code to make the test pass
+- Don't worry about perfect code yet
+- Simplest solution that works
+- It's OK to hardcode initially
+
+### 🔵 **REFACTOR: Improve the Code**
+Clean up both test and production code
+- Remove duplication
+- Improve names
+- Extract functions/classes
+- Optimize if needed
+- Tests must still pass
+
+### ♻️ **REPEAT**
+Continue the cycle for the next piece of functionality
+
+## TDD Workflow
+
+### Starting a New Feature
+```
+1. [ ] Write a list of test cases to implement
+2. [ ] Pick the simplest test case
+3. [ ] Write a failing test (RED)
+4. [ ] Run the test - verify it fails
+5. [ ] Write minimal code to pass (GREEN)
+6. [ ] Run the test - verify it passes
+7. [ ] Refactor (REFACTOR)
+8. [ ] Run tests - verify still passing
+9. [ ] Pick next test case
+10. [ ] Repeat
+```
+
+### Test Case Brainstorming
+Before coding, list out test scenarios:
+```
+Feature: User Login
+
+Test Cases:
+- [ ] Valid credentials → success
+- [ ] Invalid password → error
+- [ ] Nonexistent user → error
+- [ ] Empty email → validation error
+- [ ] Empty password → validation error
+- [ ] SQL injection attempt → sanitized
+- [ ] Rate limiting → too many attempts blocked
+- [ ] Session creation on success
+- [ ] Failed attempts logged
+```
+
+## Writing Good Tests
+
+### The AAA Pattern
+```javascript
+test('should calculate total price with tax', () => {
+  // ARRANGE: Set up test data
+  const items = [
+    { price: 10, quantity: 2 },
+    { price: 5, quantity: 1 }
+  ];
+  const taxRate = 0.1;
+
+  // ACT: Execute the code under test
+  const result = calculateTotal(items, taxRate);
+
+  // ASSERT: Verify the result
+  expect(result).toBe(27.5); // (10*2 + 5*1) * 1.1
+});
+```
+
+### Test Naming Conventions
+```
+Good test names are descriptive and follow patterns:
+
+Pattern 1: should_ExpectedBehavior_When_StateUnderTest
+  ✓ should_ReturnZero_When_CartIsEmpty
+  ✓ should_ThrowError_When_PriceIsNegative
+
+Pattern 2: When_StateUnderTest_Expect_ExpectedBehavior
+  ✓ When_CartIsEmpty_Expect_ZeroTotal
+  ✓ When_PriceIsNegative_Expect_Error
+
+Pattern 3: GivenContext_WhenAction_ThenOutcome
+  ✓ GivenEmptyCart_WhenCalculatingTotal_ThenReturnsZero
+  ✓ GivenInvalidPrice_WhenCalculating_ThenThrowsError
+```
+
+### Test Organization
+```javascript
+describe('ShoppingCart', () => {
+  describe('addItem', () => {
+    it('should add item to empty cart', () => { });
+    it('should increment quantity for existing item', () => { });
+    it('should throw error for negative quantity', () => { });
+  });
+
+  describe('removeItem', () => {
+    it('should remove item from cart', () => { });
+    it('should do nothing if item not in cart', () => { });
+  });
+
+  describe('calculateTotal', () => {
+    it('should return 0 for empty cart', () => { });
+    it('should sum all item prices', () => { });
+    it('should apply tax rate correctly', () => { });
+  });
+});
+```
+
+## Types of Tests
+
+### 1. **Unit Tests**
+Test individual functions/methods in isolation
+```javascript
+// Testing a pure function
+describe('formatCurrency', () => {
+  it('should format USD correctly', () => {
+    expect(formatCurrency(1234.56, 'USD')).toBe('$1,234.56');
+  });
+
+  it('should handle zero', () => {
+    expect(formatCurrency(0, 'USD')).toBe('$0.00');
+  });
+
+  it('should round to 2 decimals', () => {
+    expect(formatCurrency(1.234, 'USD')).toBe('$1.23');
+  });
+});
+```
+
+### 2. **Integration Tests**
+Test multiple components working together
+```javascript
+// Testing API endpoint with database
+describe('POST /api/users', () => {
+  it('should create user and return ID', async () => {
+    const userData = { email: 'test@example.com', name: 'Test' };
+    const response = await request(app).post('/api/users').send(userData);
+
+    expect(response.status).toBe(201);
+    expect(response.body).toHaveProperty('id');
+
+    // Verify in database
+    const user = await db.users.findById(response.body.id);
+    expect(user.email).toBe(userData.email);
+  });
+});
+```
+
+### 3. **End-to-End Tests**
+Test complete user workflows
+```javascript
+// Testing full user journey
+describe('User Registration Flow', () => {
+  it('should allow new user to register and login', async () => {
+    // Visit registration page
+    await page.goto('/register');
+
+    // Fill form
+    await page.fill('#email', 'newuser@example.com');
+    await page.fill('#password', 'SecurePass123!');
+    await page.click('button[type="submit"]');
+
+    // Should redirect to dashboard
+    await expect(page).toHaveURL('/dashboard');
+    await expect(page.locator('.welcome-message')).toContainText('Welcome');
+  });
+});
+```
+
+## Test Doubles (Mocks, Stubs, Spies)
+
+### When to Use Mocks
+```javascript
+// Mock external dependencies for unit tests
+describe('UserService', () => {
+  it('should send welcome email on registration', async () => {
+    // Mock the email service
+    const mockEmailService = {
+      send: jest.fn().mockResolvedValue(true)
+    };
+
+    const userService = new UserService(mockEmailService);
+    await userService.registerUser({ email: 'test@example.com' });
+
+    // Verify email was sent
+    expect(mockEmailService.send).toHaveBeenCalledWith({
+      to: 'test@example.com',
+      template: 'welcome'
+    });
+  });
+});
+```
+
+### Dependency Injection for Testability
+```typescript
+// Bad: Hard to test
+class UserService {
+  async createUser(data: UserData) {
+    await Database.save(data); // Direct dependency
+    await EmailService.send(data.email); // Hard to mock
+  }
+}
+
+// Good: Easy to test
+class UserService {
+  constructor(
+    private db: DatabaseService,
+    private email: EmailService
+  ) {}
+
+  async createUser(data: UserData) {
+    await this.db.save(data);
+    await this.email.send(data.email);
+  }
+}
+
+// Now we can inject mocks in tests
+```
+
+## TDD Anti-Patterns to Avoid
+
+### ❌ **Testing Implementation Details**
+```javascript
+// Bad: Tests implementation
+test('should call helper function 3 times', () => {
+  const spy = jest.spyOn(obj, 'helperFunc');
+  obj.mainFunc();
+  expect(spy).toHaveBeenCalledTimes(3);
+});
+
+// Good: Tests behavior
+test('should return correct result', () => {
+  expect(obj.mainFunc()).toBe(expectedResult);
+});
+```
+
+### ❌ **Overly Complex Tests**
+```javascript
+// Bad: Test is harder to understand than the code
+test('complex test', () => {
+  const data = generateComplexData();
+  for (let i = 0; i < data.length; i++) {
+    if (data[i].type === 'A') {
+      // ... complex logic
+    }
+  }
+  expect(result).toBe(/* computed value */);
+});
+
+// Good: Simple, focused test
+test('should process type A items correctly', () => {
+  const item = { type: 'A', value: 10 };
+  expect(processItem(item)).toBe(20);
+});
+```
+
+### ❌ **Test Interdependence**
+```javascript
+// Bad: Tests depend on each other
+let userId;
+test('create user', () => {
+  userId = createUser(); // Side effect
+});
+test('update user', () => {
+  updateUser(userId); // Depends on previous test
+});
+
+// Good: Each test is independent
+test('create user', () => {
+  const userId = createUser();
+  expect(userId).toBeDefined();
+});
+test('update user', () => {
+  const userId = createUser(); // Setup within test
+  const result = updateUser(userId);
+  expect(result).toBe(true);
+});
+```
+
+## Test Coverage Targets
+
+### Aim for High Coverage, Not 100%
+- **Statements**: 80%+ (most lines executed)
+- **Branches**: 75%+ (most if/else paths tested)
+- **Functions**: 90%+ (most functions tested)
+- **Lines**: 80%+ (most lines covered)
+
+### What to Prioritize
+1. **Critical business logic** - Must have 100% coverage
+2. **Complex algorithms** - High coverage with edge cases
+3. **Public APIs** - All entry points tested
+4. **Error handling** - All error paths verified
+
+### What's OK to Skip
+- Trivial getters/setters
+- Framework boilerplate
+- Third-party library code
+- Configuration files
+
+## TDD Best Practices
+
+### 1. **Write Tests First** (Truly!)
+```
+❌ Bad: Write code first, then add tests
+✓ Good: Write failing test, then make it pass
+```
+
+### 2. **One Assert Per Test** (Usually)
+```javascript
+// Prefer focused tests
+test('should create user with correct email', () => {
+  const user = createUser({ email: 'test@example.com' });
+  expect(user.email).toBe('test@example.com');
+});
+
+test('should create user with hashed password', () => {
+  const user = createUser({ password: 'secret' });
+  expect(user.password).not.toBe('secret');
+  expect(user.password).toMatch(/^\$2[aby]\$/);
+});
+```
+
+### 3. **Fast Tests**
+```
+- Unit tests: < 10ms each
+- Integration tests: < 100ms each
+- E2E tests: < 5s each
+
+If slower, consider:
+- Using test doubles
+- Running in parallel
+- Optimizing setup/teardown
+```
+
+### 4. **Reliable Tests**
+```
+Tests should:
+- ✓ Pass consistently (no flakiness)
+- ✓ Fail for the right reasons
+- ✓ Be deterministic
+- ✓ Not depend on external state
+- ✓ Clean up after themselves
+```
+
+### 5. **Readable Tests**
+```javascript
+// Tests are documentation - make them clear
+test('should allow user to checkout with valid cart', () => {
+  // Arrange: Create a realistic scenario
+  const cart = createCart();
+  cart.addItem({ id: 1, name: 'Widget', price: 9.99 });
+  const user = createUser({ hasPaymentMethod: true });
+
+  // Act: Perform the action
+  const result = checkout(cart, user);
+
+  // Assert: Verify expected outcome
+  expect(result.status).toBe('success');
+  expect(result.orderId).toBeDefined();
+});
+```
+
+## TDD Workflow with Todo System
+
+```
+When implementing a feature with TDD:
+
+Feature: Shopping Cart
+
+[ ] Write test cases list
+[ ] RED: Test for adding first item
+[ ] GREEN: Implement add item (simple)
+[ ] REFACTOR: Clean up code
+[ ] RED: Test for adding duplicate item
+[ ] GREEN: Implement quantity increment
+[ ] REFACTOR: Extract logic
+[ ] RED: Test for removing item
+[ ] GREEN: Implement remove item
+[ ] REFACTOR: Final cleanup
+[ ] Verify all tests pass
+[ ] Check coverage report
+```
+
+## When to Use This Skill
+
+- When starting any new feature or function
+- When fixing bugs (write test that reproduces bug first)
+- When refactoring (tests ensure behavior doesn't change)
+- When code quality and reliability are critical
+- When you want to move fast with confidence
+
+## Example: TDD Session
+
+```
+Task: Implement a function to validate email addresses
+
+TEST LIST:
+- [ ] Valid email with standard format
+- [ ] Invalid email without @
+- [ ] Invalid email without domain
+- [ ] Empty string
+- [ ] Null/undefined input
+- [ ] Email with special characters
+- [ ] Email with subdomain
+
+---
+
+🔴 RED - Test 1:
+```javascript
+test('should return true for valid email', () => {
+  expect(isValidEmail('user@example.com')).toBe(true);
+});
+// ❌ FAILS: isValidEmail is not defined
+```
+
+🟢 GREEN - Minimal implementation:
+```javascript
+function isValidEmail(email) {
+  return email === 'user@example.com'; // Hardcoded!
+}
+// ✅ PASSES
+```
+
+🔴 RED - Test 2:
+```javascript
+test('should return false for email without @', () => {
+  expect(isValidEmail('userexample.com')).toBe(false);
+});
+// ❌ FAILS: Returns true (because of hardcode)
+```
+
+🟢 GREEN - Real implementation:
+```javascript
+function isValidEmail(email) {
+  return email.includes('@');
+}
+// ✅ PASSES both tests
+```
+
+🔴 RED - Test 3:
+```javascript
+test('should return false for empty string', () => {
+  expect(isValidEmail('')).toBe(false);
+});
+// ❌ FAILS
+```
+
+🟢 GREEN - Improved:
+```javascript
+function isValidEmail(email) {
+  return email && email.includes('@') && email.includes('.');
+}
+// ✅ PASSES all tests
+```
+
+🔵 REFACTOR - Polish:
+```javascript
+function isValidEmail(email) {
+  if (!email) return false;
+  const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
+  return emailRegex.test(email);
+}
+// ✅ PASSES all tests, cleaner implementation
+```
+
+Continue with remaining test cases...
+```
+
+---
+
+**Remember**: TDD feels slower at first, but pays dividends in fewer bugs, better design, and faster debugging. Trust the process!

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