12-factor-app
Skill4 starsChanged 3 months agoApache-2.0View on GitHub
Load when designing, building, or reviewing SaaS, cloud-native apps, microservices, containerized workloads, or serverless functions — or when the user mentions 12-factor, config in env, stateless processes, or dev/prod parity.
- Reads credentials
- Installs packages
In this repository35 other files it gives its agents.
- AGENTS.mdAGENTS.md
- caveman-commitSkill
- caveman-reviewSkill
- cavemanSkill
- conventional-commitsSkill
- creating-pull-requestsSkill
- deep-researchSkill
- dispatching-parallel-agentsSkill
- domain-modelingSkill
- finishing-a-development-branchSkill
- forge-cleanupSkill
- forge-docsSkill
- forge-eu-accessibilitySkill
- forge-flowSkill
- forge-initSkill
- forge-seoSkill
- forge-setupSkill
- forgeSkill
- forge-tailwindcss-conventionsSkill
- frontend-designSkill
- git-issue-trackerSkill
- grillingSkill
- kiss-principleSkill
- loopsSkill
- planning-and-task-breakdownSkill
- prototypeSkill
- pr-resolveSkill
- pr-reviewSkill
- resolving-merge-conflictsSkill
- ste100Skill
- subagent-driven-developmentSkill
- use-git-identitySkill
- using-git-worktreesSkill
- verification-before-completionSkill
- wayfinderSkill
The file
We split this skill into the rules it gives an agent
1 rule. About 0 are common, 1 is distinctive, and 0 are very specific to this project.
≈0
Common · estimate
Many files like this have a rule of this kind.
≈1
Distinctive · estimate
This author's own choices. Worth a look.
0
Very specific
Tied to their project's names, files or tools. Probably skip.
- Common
- Distinctive
- Very specific
- Distinctive: line 43
Check each factor systematically against the checklist above
≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.
Files
12-Factor App
Heroku's methodology for building portable, scalable, maintainable SaaS apps. Language-agnostic. Modern extensions: observability, API-first, security, progressive delivery, auth, sustainability.
The 12 Factors (Original)
| # | Factor | Core Rule | Agent Check |
| I | Codebase | One repo per app, many deploys | Single source of truth; IaC in same repo |
| II | Dependencies | Explicitly declare and isolate | Manifest + lockfile; no system-wide deps; exact Docker base image versions |
| III | Config | Store in environment | Env vars / config systems; secrets in Vault/K8s Secrets; never in code |
| IV | Backing Services | Treat as attached resources | URL-based config; swappable local → managed; circuit breakers + retries |
| V | Build, Release, Run | Strictly separate stages | Immutable releases tagged with unique ID; no builds in production |
| VI | Processes | Stateless, share-nothing | No in-memory sessions; no local persistent writes; multiple instances concurrent |
| VII | Port Binding | Self-contained, export via port | Configurable port; standalone without external web server |
| VIII | Concurrency | Scale out via process model | Horizontal scaling; separate web/worker process types; no single points of failure |
| IX | Disposability | Fast startup, graceful shutdown | <30s startup (ideally <10s); SIGTERM handling; cattle, not pets |
| X | Dev/Prod Parity | Keep environments similar | Same DB type/version; Docker/IaC for parity; one-command local dev |
| XI | Logs | Treat as event streams | stdout only; structured (JSON); no log file management in app code |
| XII | Admin Processes | Run as one-off processes | Same codebase/config as app; never inside web/worker processes |
Modern Extensions
| # | Factor | Core Rule |
| XIII | Observability | OpenTelemetry, metrics, traces, structured logs, SLIs/SLOs |
| XIV | API-First | Contract-first design (OpenAPI/gRPC); consumers generate from spec |
| XV | Security | SBOM, image signing, zero-trust, secrets rotation, dependency scanning |
| XVI | Progressive Delivery | Feature flags, canary releases, blue/green deployments |
| XVII | Auth/AuthZ | Externalized identity (OIDC/OAuth2), RBAC/ABAC, service-to-service mTLS |
| XVIII | Sustainability | FinOps, right-sizing, carbon-aware computing |
Agent Evaluation Flow
- Identify deployment model (VM, container, serverless, edge)
- Check each factor systematically against the checklist above
- Distinguish violations from mitigations
- Prioritize by impact: Config, Processes, Build/Release/Run are most critical
- Suggest concrete fixes: "replace X with Y using Z approach"
Common Mistakes
| Mistake | Fix |
Secrets in .env committed to git | Use Vault, K8s Secrets, or cloud provider secret managers |
const sessions = {} in memory | Redis or database for session storage |
npm install && npm build && npm start in Dockerfile | Multi-stage Docker build; compile in stage 1, run pre-built artifact in stage 2 |
| Hardcoded DB URLs | os.environ.get("DATABASE_URL") |
| File-based logging | ConsoleHandler() → stdout |
| 2+ minute startup times | Lazy-load heavy resources; defer to background workers |
Related Principles
- KISS — simplicity in design and implementation
- Unix Philosophy — do one thing well, compose with text streams
- Infrastructure as Code — declarative infrastructure management
- DRY — eliminate duplication without over-abstraction
- YAGNI — defer unnecessary features
Source
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