12 Factor Apps Agent Skill

12-Factor App Compliance Analysis

> Reference: The Twelve-Factor App

Overview

The 12-Factor App methodology is a set of best practices for building Software-as-a-Service applications that are:

• Portable across execution environments
• Scalable without architectural changes
• Suitable for continuous deployment
• Maintainable with minimal friction

Input Parameters

| Parameter | Description | Required |

|-----------|-------------|----------|

| codebase_path | Root path of the codebase to analyze | Required |

Analysis Framework

Factor I: Codebase

Principle: One codebase tracked in revision control, many deploys.

Search Patterns:

# Check for version control
ls -la .git 2>/dev/null || ls -la .hg 2>/dev/null

# Check for multiple apps sharing codebase
find . -name "package.json" -o -name "pyproject.toml" -o -name "setup.py" | head -20

# Check for environment-specific code branches
grep -r "if.*production\|if.*development\|if.*staging" --include="*.py" --include="*.js" --include="*.ts"

File Patterns: .git/, package.json, pyproject.toml, deployment configs

Compliance Criteria:

| Level | Criteria |

|-------|----------|

| Strong | Single Git repo, same codebase for all environments, no env-specific code branches |

| Partial | Single repo but some environment-specific code paths |

| Weak | Multiple repos for same app or significant code duplication across environments |

Anti-patterns:

• Multiple Git repositories for the same application
• Environment-specific code branches (if production: ...)
• Different source files for dev vs prod
• Shared code not extracted to libraries

Factor II: Dependencies

Principle: Explicitly declare and isolate dependencies.

Search Patterns:

# Python dependency files
find . -name "requirements.txt" -o -name "pyproject.toml" -o -name "setup.py" -o -name "Pipfile" -o -name "uv.lock"

# JavaScript/TypeScript dependency files
find . -name "package.json" -o -name "package-lock.json" -o -name "yarn.lock" -o -name "pnpm-lock.yaml"

# Check for system tool assumptions
grep -r "subprocess.*curl\|subprocess.*wget\|os.system.*ffmpeg\|shutil.which" --include="*.py"
grep -r "exec.*curl\|child_process.*curl" --include="*.js" --include="*.ts"

# Docker/container isolation
find . -name "Dockerfile" -o -name "docker-compose*.yml"

File Patterns: /requirements*.txt, /package.json, /*.lock, /Dockerfile

Compliance Criteria:

| Level | Criteria |

|-------|----------|

| Strong | Lock files present, dependency isolation (venv/Docker), no implicit system tools |

| Partial | Dependencies declared but no lock files or isolation |

| Weak | Dependencies in documentation only, relies on system-installed packages |

Anti-patterns:

• Missing lock files (non-deterministic builds)
• Assuming system tools (curl, ImageMagick, ffmpeg) are available
• Different dependency managers in dev vs production
• No virtual environment or container isolation

Factor III: Config

Principle: Store config in the environment.

Search Patterns:

# Environment variable usage
grep -r "os.environ\|os.getenv\|process.env\|ENV\[" --include="*.py" --include="*.js" --include="*.ts" --include="*.rb"

# Hardcoded credentials (anti-pattern)
grep -r "password.*=.*['\"]" --include="*.py" --include="*.js" --include="*.ts" | grep -v "test\|spec\|example"
grep -r "api_key.*=.*['\"]" --include="*.py" --include="*.js" --include="*.ts" | grep -v "test\|spec\|example"
grep -r "secret.*=.*['\"]" --include="*.py" --include="*.js" --include="*.ts" | grep -v "test\|spec\|example"

# Environment-specific config files (anti-pattern)
find . -name "config.dev.*" -o -name "config.prod.*" -o -name "settings.development.*" -o -name "settings.production.*"

# Database URLs in code
grep -r "postgresql://\|mysql://\|mongodb://\|redis://" --include="*.py" --include="*.js" --include="*.ts" | grep -v ".env\|test\|example"

File Patterns: /.env*, /config/*.py, **/settings.py, environment files

Compliance Criteria:

| Level | Criteria |

|-------|----------|

| Strong | All config via environment variables, no hardcoded secrets, could open-source without leaks |

| Partial | Most config externalized but some hardcoded defaults |

| Weak | Hardcoded credentials, environment-specific config files |

Anti-patterns:

• Hardcoded database URLs, API keys, passwords in source
• Config files like config/production.yml vs config/development.yml
• Environment grouping (if ENV == 'production': ...)
• Secrets committed to version control

Factor IV: Backing Services

Principle: Treat backing services as attached resources.

Search Patterns:

# Database connection via config
grep -r "DATABASE_URL\|DB_HOST\|REDIS_URL\|CACHE_URL" --include="*.py" --include="*.js" --include="*.ts"

# Service initialization
grep -r "create_engine\|MongoClient\|Redis\|Celery\|boto3" --include="*.py"
grep -r "createPool\|createClient\|new Redis\|S3Client" --include="*.js" --include="*.ts"

# Hardcoded service locations (anti-pattern)
grep -r "localhost:5432\|localhost:6379\|localhost:27017\|127.0.0.1" --include="*.py" --include="*.js" --include="*.ts" | grep -v "test\|spec\|example\|default"

File Patterns: /database/*.py, /services/*.py, **/db.py, connection configurations

Compliance Criteria:

| Level | Criteria |

|-------|----------|

| Strong | All services via URL/connection string in config, swappable without code changes |

| Partial | Most services configurable but some hardcoded defaults |

| Weak | Hardcoded service locations, different code paths per environment |

Anti-patterns:

• Hardcoded localhost for services in production code
• Conditional logic for local vs cloud services (if USE_S3: ... else: local_storage)
• Service-specific code paths based on environment
• Different drivers for dev vs prod

Factor V: Build, Release, Run

Principle: Strictly separate build and run stages.

Search Patterns:

# Build/deploy configuration
find . -name "Dockerfile" -o -name "Makefile" -o -name "build.sh" -o -name "deploy.sh"
find . -name ".github/workflows/*.yml" -o -name ".gitlab-ci.yml" -o -name "Jenkinsfile"

# Build scripts in package.json
grep -A5 '"scripts"' package.json 2>/dev/null | grep -E "build|start|deploy"

# Check for runtime compilation (anti-pattern)
grep -r "compile\|transpile\|webpack" --include="*.py" | grep -v "test\|build"

File Patterns: /Dockerfile, /Makefile, /.github/workflows/, CI/CD configs

Compliance Criteria:

| Level | Criteria |

|-------|----------|

| Strong | Immutable releases, clear build/release/run stages, unique release IDs |

| Partial | Build and run separated but release not immutable |

| Weak | Runtime code modifications, asset compilation at startup |

Anti-patterns:

• Runtime code modifications
• Asset compilation during application startup
• Configuration baked into build artifacts
• No release versioning

Factor VI: Processes

Principle: Execute the app as one or more stateless processes.

Search Patterns:

# Session storage patterns
grep -r "session\|Session" --include="*.py" --include="*.js" --include="*.ts" | head -20

# In-process state (anti-pattern)
grep -r "global.*cache\|process_local\|instance_cache" --include="*.py"
grep -r "global\..*=\|module\.exports\.cache" --include="*.js" --include="*.ts"

# External session stores (good pattern)
grep -r "redis.*session\|memcached.*session\|session.*redis" --include="*.py" --include="*.js" --include="*.ts"

# Sticky session configuration (anti-pattern)
grep -r "sticky.*session\|session.*affinity" --include="*.yml" --include="*.yaml" --include="*.json"

File Patterns: /middleware/*.py, /session/*.py, server configurations

Compliance Criteria:

| Level | Criteria |

|-------|----------|

| Strong | Stateless processes, all state in external datastores (Redis, DB) |

| Partial | Mostly stateless but some in-process caching |

| Weak | Sticky sessions, in-process session storage, shared memory state |

Anti-patterns:

• In-process session storage (user_sessions = {})
• Sticky sessions or session affinity
• File-based caching between requests
• Global mutable state shared across requests

Factor VII: Port Binding

Principle: Export services via port binding.

Search Patterns:

# Self-contained port binding
grep -r "app.run\|server.listen\|serve\|uvicorn" --include="*.py"
grep -r "app.listen\|server.listen\|createServer" --include="*.js" --include="*.ts"

# PORT environment variable
grep -r "PORT\|port" --include="*.py" --include="*.js" --include="*.ts" | grep -i "environ\|process.env"

# Webserver as dependency
grep -r "uvicorn\|gunicorn\|flask\|fastapi\|express\|koa\|hapi" package.json pyproject.toml requirements.txt 2>/dev/null

File Patterns: /main.py, /server.py, /app.py, /index.js

Compliance Criteria:

| Level | Criteria |

|-------|----------|

| Strong | Self-contained app binds to PORT, webserver is a dependency |

| Partial | Port binding but not configurable via environment |

| Weak | Relies on external webserver container (Apache, Nginx) to provide HTTP |

Anti-patterns:

• Relying on Apache/Nginx/Tomcat to inject webserver functionality
• Hardcoded port numbers
• No PORT environment variable support
• CGI scripts or server modules

Factor VIII: Concurrency

Principle: Scale out via the process model.

Search Patterns:

# Process definitions
find . -name "Procfile" -o -name "process.yml" -o -name ".foreman"

# Multiple entry points
find . -name "worker.py" -o -name "scheduler.py" -o -name "web.py"

# Background job systems
grep -r "celery\|rq\|sidekiq\|bull\|agenda" --include="*.py" --include="*.js" --include="*.ts"
grep -r "Celery\|Worker\|BackgroundJob" --include="*.py" --include="*.js" --include="*.ts"

File Patterns: /Procfile, /worker.py, **/scheduler.py, queue configurations

Compliance Criteria:

| Level | Criteria |

|-------|----------|

| Strong | Explicit process types (web, worker, scheduler), horizontal scaling |

| Partial | Multiple process types but not easily scalable |

| Weak | Single monolithic process, no separation of concerns |

Anti-patterns:

• Single process handling all workloads
• Hard-coded worker counts in code
• No separation between web and background processes
• Vertical scaling only (bigger server, not more processes)

Factor IX: Disposability

Principle: Maximize robustness with fast startup and graceful shutdown.

Search Patterns:

# Signal handlers
grep -r "signal.signal\|SIGTERM\|SIGINT\|atexit" --include="*.py"
grep -r "process.on.*SIGTERM\|process.on.*SIGINT" --include="*.js" --include="*.ts"

# Graceful shutdown
grep -r "graceful.*shutdown\|shutdown_handler\|cleanup" --include="*.py" --include="*.js" --include="*.ts"

# Startup time
grep -r "startup\|initialize\|bootstrap" --include="*.py" --include="*.js" --include="*.ts" | head -20

File Patterns: /main.py, /server.py, lifecycle management code

Compliance Criteria:

| Level | Criteria |

|-------|----------|

| Strong | Fast startup (<10s), SIGTERM handling, graceful shutdown, jobs returnable to queue |

| Partial | Graceful shutdown but slow startup |

| Weak | No signal handling, jobs lost on process death, slow startup |

Anti-patterns:

• No SIGTERM/SIGINT handlers
• Slow startup (>30 seconds)
• Jobs lost if process crashes
• No cleanup on shutdown

Factor X: Dev/Prod Parity

Principle: Keep development, staging, and production as similar as possible.

Search Patterns:

# Different services per environment (anti-pattern)
grep -r "if.*development.*sqlite\|if.*production.*postgres" --include="*.py" --include="*.js" --include="*.ts"
grep -r "development.*SQLite\|production.*PostgreSQL" --include="*.py" --include="*.js" --include="*.ts"

# Docker for parity
find . -name "docker-compose*.yml" -o -name "Dockerfile"

# Environment-specific backends
grep -r "USE_LOCAL_\|LOCAL_STORAGE\|MOCK_" --include="*.py" --include="*.js" --include="*.ts"

File Patterns: **/docker-compose*.yml, environment configurations

Compliance Criteria:

| Level | Criteria |

|-------|----------|

| Strong | Same services everywhere (PostgreSQL in dev and prod), containerized |

| Partial | Mostly same but some lightweight dev alternatives |

| Weak | SQLite in dev, PostgreSQL in prod; different backing services |

Anti-patterns:

• SQLite for development, PostgreSQL for production
• In-memory cache in dev, Redis in prod
• Different service versions across environments
• "It works on my machine" issues

Factor XI: Logs

Principle: Treat logs as event streams.

Search Patterns:

# Stdout logging
grep -r "print(\|logging.info\|logger.info\|console.log" --include="*.py" --include="*.js" --include="*.ts" | head -20

# File-based logging (anti-pattern)
grep -r "FileHandler\|open.*\.log\|writeFile.*log\|fs.appendFile.*log" --include="*.py" --include="*.js" --include="*.ts"
grep -r "/var/log\|/tmp/.*\.log\|logs/" --include="*.py" --include="*.js" --include="*.ts" | grep -v "test\|example"

# Structured logging
grep -r "structlog\|json_logger\|pino\|winston" --include="*.py" --include="*.js" --include="*.ts"

File Patterns: /logging.py, /logger.py, logging configurations

Compliance Criteria:

| Level | Criteria |

|-------|----------|

| Strong | Unbuffered stdout only, structured logging (JSON), no file management |

| Partial | Stdout logging but with some file handlers |

| Weak | Application writes to log files, manages rotation |

Anti-patterns:

• Writing logs to files (FileHandler, open('/var/log/app.log'))
• Log rotation logic in application code
• Log archival managed by application
• Buffered logging

Factor XII: Admin Processes

Principle: Run admin/management tasks as one-off processes.

Search Patterns:

# Management commands
find . -name "manage.py" -o -name "Rakefile" -o -name "artisan"
grep -r "@cli.command\|@click.command\|typer.command" --include="*.py"

# Migration scripts
find . -name "migrations" -type d
find . -name "*migration*.py" -o -name "*migrate*.py"

# Admin scripts with proper isolation
grep -r "bundle exec\|source.*venv\|uv run" --include="*.sh" --include="Makefile"

File Patterns: /manage.py, /cli.py, /migrations/, admin scripts

Compliance Criteria:

| Level | Criteria |

|-------|----------|

| Strong | Admin tasks use same dependencies/config, proper isolation, idempotent |

| Partial | Admin tasks exist but different setup from app |

| Weak | Manual database manipulation, scripts without isolation |

Anti-patterns:

• Admin scripts not using app's dependency manager
• Direct SQL manipulation outside of migrations
• Admin scripts with hardcoded credentials
• Non-idempotent migrations

Output Format

Executive Summary Table

| Factor | Status | Notes |
|--------|--------|-------|
| I. Codebase | **Strong/Partial/Weak** | [Key finding] |
| II. Dependencies | **Strong/Partial/Weak** | [Key finding] |
| III. Config | **Strong/Partial/Weak** | [Key finding] |
| IV. Backing Services | **Strong/Partial/Weak** | [Key finding] |
| V. Build/Release/Run | **Strong/Partial/Weak** | [Key finding] |
| VI. Processes | **Strong/Partial/Weak** | [Key finding] |
| VII. Port Binding | **Strong/Partial/Weak** | [Key finding] |
| VIII. Concurrency | **Strong/Partial/Weak** | [Key finding] |
| IX. Disposability | **Strong/Partial/Weak** | [Key finding] |
| X. Dev/Prod Parity | **Strong/Partial/Weak** | [Key finding] |
| XI. Logs | **Strong/Partial/Weak** | [Key finding] |
| XII. Admin Processes | **Strong/Partial/Weak** | [Key finding] |

**Overall**: X Strong, Y Partial, Z Weak

Per-Factor Analysis

For each factor, provide:

• Current Implementation
• Evidence with file:line references
• Code snippets showing patterns

• Compliance Level
• Strong/Partial/Weak with justification

• Gaps
• What's missing vs. 12-Factor ideal

• Recommendations
• Actionable improvements with code examples

Analysis Workflow

• Initial Scan
• Run search patterns for all factors
• Identify key files for each factor
• Note any existing compliance documentation

• Deep Dive (per factor)
• Read identified files
• Evaluate against compliance criteria
• Document evidence with file paths

• Gap Analysis
• Compare current vs. 12-Factor ideal
• Identify anti-patterns present
• Prioritize by impact

• Recommendations
• Provide actionable improvements
• Include before/after code examples
• Reference best practices

• Summary
• Compile executive summary table
• Highlight strengths and critical gaps
• Suggest priority order for improvements

Quick Reference: Compliance Scoring

| Score | Meaning | Action |

|-------|---------|--------|

| Strong | Fully implements principle | Maintain, minor optimizations |

| Partial | Some implementation, significant gaps | Planned improvements |

| Weak | Minimal or no implementation | High priority for roadmap |

When to Use This Skill

• Evaluating new SaaS applications
• Reviewing cloud-native architecture decisions
• Auditing production applications for scalability
• Planning migration to cloud platforms
• Comparing application architectures
• Preparing for containerization/Kubernetes deployment