Overview

This skill provides systematic approaches for validating full-stack applications with multiple interconnected components. It enables automatic detection of project structure, parallel validation workflows, cross-component verification, and identification of integration issues.

When to use: Full-stack projects with backend + frontend, microservices, monorepos, Docker Compose setups, or any multi-technology application.

Key innovation: Parallel validation with cross-component awareness - validates each layer independently while ensuring they work together correctly.

Project Structure Detection

Detection Patterns

Monorepo Indicators:

• Root package.json with workspaces
• lerna.json or nx.json present
• Multiple package.json files in subdirectories
• pnpm-workspace.yaml present

Separate Repos Indicators:

• Single technology stack per repository
• Docker Compose references external services
• Git submodules present

Technology Stack Detection:

Backend:
- FastAPI: requirements.txt with 'fastapi', main.py with FastAPI app
- Django: manage.py, settings.py present
- Express: package.json with 'express', app.js/index.js
- Spring Boot: pom.xml or build.gradle with spring-boot

Frontend:
- React: package.json with 'react', src/App.tsx or src/App.jsx
- Vue: package.json with 'vue', src/App.vue
- Angular: package.json with '@angular/core', angular.json
- Svelte: package.json with 'svelte', src/App.svelte

Database:
- PostgreSQL: requirements.txt with 'psycopg2', docker-compose.yml with postgres
- MySQL: package.json with 'mysql2', docker-compose.yml with mysql
- MongoDB: package.json with 'mongoose', docker-compose.yml with mongo
- Redis: docker-compose.yml with redis, requirements.txt with 'redis'

Infrastructure:
- Docker: Dockerfile, docker-compose.yml present
- Kubernetes: k8s/ or kubernetes/ directory with .yaml files
- Terraform: .tf files present
- Nginx: nginx.conf present

Validation Workflows

Backend Validation Checklist

Python/FastAPI Projects:

1. Dependency validation

   • Check requirements.txt exists and is parseable
   • Verify all imports can be resolved
   • Check for version conflicts
   • Validate Python version compatibility

2. Type checking

   • Run mypy on all source files
   • Check for missing type hints
   • Validate Pydantic model definitions
   • Verify return type annotations

3. Test validation

   • Run pytest with coverage
   • Check test isolation (database cleanup)
   • Validate fixture dependencies
   • Ensure no test data pollution
   • Check for views/triggers blocking teardown

4. API schema validation

   • Extract OpenAPI/Swagger schema
   • Validate all endpoints have docstrings
   • Check request/response models
   • Verify authentication decorators

5. Database migration validation

   • Check Alembic migrations are sequential
   • Validate up/down migration pairs
   • Ensure migrations are reversible
   • Check for data loss risks

Node.js/Express Projects:

1. Dependency validation (npm/yarn/pnpm)
2. ESLint validation
3. Jest/Mocha test execution
4. API route validation
5. Database migration validation (Knex/Sequelize)

Frontend Validation Checklist

React + TypeScript Projects:

1. TypeScript validation

   • Run tsc --noEmit for type checking
   • Detect unused imports (auto-fix available)
   • Check tsconfig.json strictness
   • Validate path aliases (@/ imports)
   • Generate missing .d.ts files (vite-env.d.ts, etc.)

2. Dependency validation

   • Check package.json for peer dependency warnings
   • Detect version mismatches (React Query vs React)
   • Validate ESM vs CommonJS consistency
   • Check for deprecated packages

3. Build validation

   • Run production build (npm run build / vite build)
   • Check bundle size (warn if > 1MB per chunk)
   • Validate environment variables
   • Check for build warnings
   • Validate asset optimization

4. Code quality

   • Run ESLint with auto-fix
   • Check for console.log statements in production
   • Validate React hooks usage
   • Check for deprecated React patterns
   • Detect old library syntax (React Query v4 → v5)

5. API client validation

   • Check all API calls have error handling
   • Validate API base URLs
   • Ensure loading/error states exist
   • Check authentication token handling

Vue/Angular Projects: Similar checklist adapted to framework specifics

Database Validation Checklist

1. Schema validation

   • Check all tables exist
   • Validate foreign key constraints
   • Check for orphaned records
   • Validate indexes on frequently queried columns

2. Test isolation validation

   • Detect views dependent on test tables
   • Check for triggers that prevent cleanup
   • Validate CASCADE deletion works
   • Ensure test data doesn't leak to other tests

3. Query validation

   • Check for N+1 query problems
   • Validate JOIN efficiency
   • Check for missing indexes
   • Detect raw SQL strings (SQLAlchemy 2.0 requires text() wrapper)

Infrastructure Validation Checklist

Docker Compose Projects:

1. Service health checks

   • Verify all services start successfully
   • Check healthcheck endpoints respond
   • Validate depends_on order is correct
   • Check restart policies

2. Port conflict detection

   • Ensure no duplicate port mappings
   • Check host ports are available
   • Validate internal service communication

3. Volume validation

   • Check mounted directories exist
   • Validate volume permissions
   • Ensure persistent data volumes are defined

4. Environment variable validation

   • Check .env.example matches required vars
   • Validate all services receive needed env vars
   • Check for hardcoded credentials
   • Ensure secrets are not committed

Cross-Component Validation

API Contract Validation

Process:

1. Extract backend API schema

   • FastAPI: GET /docs → openapi.json
   • Express: Parse route definitions
   • Django REST: GET /schema

2. Extract frontend API client calls

   • Search for axios/fetch calls
   • Find API client service files
   • Parse API endpoint strings

3. Cross-validate

   • Check every frontend call has matching backend endpoint
   • Validate HTTP methods match (GET/POST/PUT/DELETE)
   • Check parameter names and types match
   • Verify response types match frontend expectations
   • Detect missing error handling

Auto-fix capabilities:

• Generate missing TypeScript types from OpenAPI schema
• Generate missing API client methods
• Update deprecated endpoint calls
• Add missing error handling

Environment Variable Consistency

Process:

1. Collect all env var references

   • Backend: os.getenv(), settings.py
   • Frontend: import.meta.env, process.env
   • Docker: docker-compose.yml env sections

2. Cross-validate

   • Check .env.example has all referenced vars
   • Ensure frontend vars have VITE_ or REACT_APP_ prefix
   • Validate no secrets in frontend code
   • Check env vars are documented

Authentication Flow Validation

Process:

1. Identify auth mechanism (JWT, OAuth, Basic, API Key)
2. Check backend auth implementation
   • Token generation/validation
   • Password hashing
   • Session management
3. Check frontend auth implementation
   • Token storage (localStorage/sessionStorage/cookies)
   • Auth headers in API calls
   • Protected route guards
   • Token refresh logic
4. Cross-validate
   • Ensure token format matches backend expectations
   • Check expiration handling
   • Validate logout clears all auth data

Parallel Validation Strategy

Execution Plan

Phase 1: Detection (Sequential)
├─ Scan project structure
├─ Identify all components
└─ Determine validation workflows

Phase 2: Component Validation (Parallel)
├─ Backend validation (background)
├─ Frontend validation (background)
├─ Database validation (background)
└─ Infrastructure validation (background)

Phase 3: Cross-Component Validation (Sequential)
├─ API contract validation (requires Phase 2 complete)
├─ Environment variable validation
└─ Authentication flow validation

Phase 4: Reporting (Sequential)
├─ Aggregate results
├─ Prioritize issues
└─ Generate recommendations

Priority Levels

Critical (🔴): Blocks deployment, requires immediate fix

• Backend tests failing
• Frontend build failing
• API contract mismatches causing runtime errors
• Database migration failures
• Security vulnerabilities

Warning (🟡): Should be fixed, doesn't block deployment

• Low test coverage (< 70%)
• Bundle size warnings
• Missing type hints
• Unused dependencies
• Performance issues

Info (🟢): Nice to have, improves quality

• Code style inconsistencies
• Missing documentation
• Optimization opportunities
• Deprecated syntax (still functional)

Auto-Fix Capabilities

Automatic Fixes (No confirmation needed)

TypeScript:

• Remove unused imports
• Add missing semicolons
• Fix indentation
• Sort imports

Python:

• Format with Black
• Sort imports with isort
• Remove unused variables (prefix with _)
• Add text() wrapper to raw SQL strings

Configuration:

• Generate missing config files (vite-env.d.ts, tsconfig.json)
• Fix ESM/CommonJS conflicts
• Update deprecated config syntax

Suggested Fixes (Requires confirmation)

TypeScript:

• Generate missing type definitions
• Update React Query v4 → v5 syntax
• Add missing error handling
• Migrate class components to hooks

Python:

• Add missing type hints
• Migrate to async/await
• Update deprecated SQLAlchemy patterns
• Add missing docstrings

Database:

• Add missing indexes
• Fix N+1 queries with joins
• Update cascade delete rules

Pattern Learning Integration

Patterns to Capture

Project Structure Patterns:

{
  "project_type": "fullstack-monorepo",
  "backend": "fastapi",
  "frontend": "react-typescript",
  "database": "postgresql",
  "infrastructure": "docker-compose",
  "patterns_detected": {
    "api_versioning": "/api/v1",
    "auth_method": "jwt",
    "orm": "sqlalchemy",
    "state_management": "react-query"
  }
}

Common Issue Patterns:

{
  "typescript_unused_imports": {
    "frequency": 12,
    "auto_fix_success_rate": 1.0,
    "common_files": ["src/components/*.tsx"]
  },
  "sqlalchemy_raw_sql": {
    "frequency": 5,
    "auto_fix_success_rate": 1.0,
    "pattern": "execute('SELECT ...') → execute(text('SELECT ...'))"
  },
  "react_query_v4_syntax": {
    "frequency": 3,
    "auto_fix_success_rate": 0.9,
    "pattern": "useQuery(['key'], fn) → useQuery({queryKey: ['key'], queryFn: fn})"
  }
}

Validation Performance Patterns:

{
  "backend_validation_time": "15s",
  "frontend_validation_time": "45s",
  "bottlenecks": ["TypeScript compilation", "npm install"],
  "optimization_opportunities": ["Use turbo for builds", "Cache dependencies"]
}

When to Apply This Skill

Automatic triggers:

• Project has both backend and frontend directories
• docker-compose.yml detected with multiple services
• Multiple package.json or requirements.txt files found
• User runs /validate-fullstack command

Manual triggers:

• User mentions "full-stack", "backend and frontend", "API integration"
• User reports issues across multiple components
• Deployment preparation
• CI/CD pipeline setup

Integration with Other Skills

Combines with:

• code-analysis: For structural analysis of each component
• quality-standards: For quality benchmarks
• testing-strategies: For test coverage validation
• pattern-learning: For capturing project-specific patterns
• validation-standards: For tool usage validation

Delegates to agents:

• frontend-analyzer: For detailed TypeScript/React validation
• api-contract-validator: For API synchronization
• build-validator: For build configuration issues
• test-engineer: For test infrastructure fixes
• quality-controller: For comprehensive quality assessment

Success Metrics

Validation effectiveness:

• Issue detection rate: % of issues found automatically
• False positive rate: < 5%
• Auto-fix success rate: > 80%
• Time savings vs manual validation: > 90%

Quality improvements:

• Issues caught before deployment: Track over time
• Deployment success rate: Should increase
• Time to fix issues: Should decrease
• Pattern reuse rate: Should increase for similar projects

Example Validation Report

✅ Full-Stack Validation Complete (2m 34s)

📊 Component Status:
├─ Backend (FastAPI + PostgreSQL)
│  ├─ ✅ Dependencies: 42 packages, 0 conflicts
│  ├─ ✅ Type hints: 98% coverage
│  ├─ ⚠️  Tests: 45 passing, 42% coverage (target: 70%)
│  └─ ✅ API schema: 23 endpoints documented
│
├─ Frontend (React + TypeScript)
│  ├─ ✅ Type check: 0 errors (auto-fixed 16)
│  ├─ ✅ Build: 882KB bundle (optimized)
│  ├─ ✅ Dependencies: 124 packages, 0 peer warnings
│  └─ ✅ Unused imports: 0 (auto-removed 5)
│
└─ Integration
   ├─ ✅ API contract: 23/23 endpoints matched
   ├─ ✅ Environment vars: 15/15 documented
   └─ ✅ Auth flow: JWT tokens validated

🔧 Auto-Fixed Issues (11):
✓ Removed 5 unused TypeScript imports
✓ Generated vite-env.d.ts
✓ Added text() wrapper to 3 SQL queries
✓ Fixed 2 React Query v5 syntax issues

⚠️  Recommended Actions (2):
1. Increase test coverage to 70% (currently 42%)
2. Add indexes to users.email and projects.created_at

🎯 Overall Score: 87/100 (Production Ready)