Environment Variable Detection
Identify all environment variables an application needs before deployment. Missing env vars are the most common cause of deployment failures.
Detection sources (check in order)
1. .env.example / .env.sample / .env.template
Primary source. Read the file and extract every variable name and any inline comments describing its purpose.
DATABASE_URL=postgresql://user:pass@localhost:5432/db
REDIS_URL=redis://localhost:6379
API_KEY=your-api-key-here
SECRET_KEY=change-me
2. Source code patterns
Use grep across the repo root for these patterns:
| Pattern |
Language |
process.env.VAR_NAME |
Node.js |
Deno.env.get("VAR_NAME") |
Deno |
os.environ["VAR_NAME"] or os.getenv("VAR_NAME") |
Python |
os.Getenv("VAR_NAME") |
Go |
ENV["VAR_NAME"] or ENV.fetch("VAR_NAME") |
Ruby |
env::var("VAR_NAME") |
Rust |
System.getenv("VAR_NAME") |
Java |
@Value("${VAR_NAME}") |
Spring |
3. Framework config files
| File |
What to look for |
next.config.js / next.config.mjs |
env: block, NEXT_PUBLIC_* prefixed vars |
nuxt.config.ts |
runtimeConfig block |
vite.config.ts |
define block, VITE_* prefixed vars |
docker-compose.yml |
environment: sections |
Dockerfile |
ENV and ARG directives |
settings.py (Django) |
os.environ calls |
config/*.yml (Rails) |
<%= ENV["VAR"] %> patterns |
4. Database/service URLs
Check dependency manifests for services that typically require connection URLs:
| Dependency |
Expected env var |
pg / sequelize / prisma / typeorm |
DATABASE_URL |
mongoose / mongodb |
MONGODB_URI |
ioredis / redis |
REDIS_URL |
@aws-sdk/* |
AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_REGION |
stripe |
STRIPE_SECRET_KEY, STRIPE_WEBHOOK_SECRET |
@sendgrid/mail |
SENDGRID_API_KEY |
nodemailer |
SMTP_HOST, SMTP_PORT, SMTP_USER, SMTP_PASS |
@auth0/* / next-auth |
AUTH_SECRET, AUTH_URL, provider-specific keys |
Classification
Classify each detected variable:
| Category |
Examples |
Required for deploy? |
| Infrastructure |
DATABASE_URL, REDIS_URL, PORT |
Yes |
| Secrets |
API_KEY, SECRET_KEY, JWT_SECRET |
Yes |
| Service URLs |
NEXT_PUBLIC_API_URL, WEBHOOK_URL |
Yes (but values differ per environment) |
| Build-time |
NEXT_PUBLIC_*, VITE_* |
Yes (must be set during build) |
| Optional/Debug |
LOG_LEVEL, DEBUG, NODE_ENV |
No (has sensible defaults) |
Build-time vs runtime
This distinction matters for Dockerfiles:
- Build-time: Set as
ARG in Dockerfile, passed via --build-arg or args: in compose. Includes NEXT_PUBLIC_*, VITE_*, and any var used during npm run build.
- Runtime: Set as
ENV in Dockerfile or environment: in compose. Includes DATABASE_URL, PORT, API keys.
Output format
After detection, report:
- List of all detected env vars with their source (
.env.example, source code, framework config)
- Classification (infrastructure, secret, service URL, build-time, optional)
- Which vars are missing values (need user input)
- Which vars have safe defaults (e.g.
PORT=3000, NODE_ENV=production)
- Which vars are build-time and must be in Dockerfile
ARG directives
Related Skills
pre-deploy-checklist — Uses env detection results to validate deployment readinessdockerfile-generation — Build-time env vars identified here need ARG directives in the Dockerfile
1---2name: env-detection3description: Detect required environment variables from source code, config files, and .env examples. Use when preparing for deployment, checking for missing env vars, or when the user asks about required environment configuration.4---56# Environment Variable Detection78Identify all environment variables an application needs before deployment. Missing env vars are the most common cause of deployment failures.910## Detection sources (check in order)1112### 1. `.env.example` / `.env.sample` / `.env.template`1314Primary source. Read the file and extract every variable name and any inline comments describing its purpose.1516```17DATABASE_URL=postgresql://user:pass@localhost:5432/db18REDIS_URL=redis://localhost:637919API_KEY=your-api-key-here20SECRET_KEY=change-me21```2223### 2. Source code patterns2425Use `grep` across the repo root for these patterns:2627| Pattern | Language |28|---------|----------|29| `process.env.VAR_NAME` | Node.js |30| `Deno.env.get("VAR_NAME")` | Deno |31| `os.environ["VAR_NAME"]` or `os.getenv("VAR_NAME")` | Python |32| `os.Getenv("VAR_NAME")` | Go |33| `ENV["VAR_NAME"]` or `ENV.fetch("VAR_NAME")` | Ruby |34| `env::var("VAR_NAME")` | Rust |35| `System.getenv("VAR_NAME")` | Java |36| `@Value("${VAR_NAME}")` | Spring |3738### 3. Framework config files3940| File | What to look for |41|------|-----------------|42| `next.config.js` / `next.config.mjs` | `env:` block, `NEXT_PUBLIC_*` prefixed vars |43| `nuxt.config.ts` | `runtimeConfig` block |44| `vite.config.ts` | `define` block, `VITE_*` prefixed vars |45| `docker-compose.yml` | `environment:` sections |46| `Dockerfile` | `ENV` and `ARG` directives |47| `settings.py` (Django) | `os.environ` calls |48| `config/*.yml` (Rails) | `<%= ENV["VAR"] %>` patterns |4950### 4. Database/service URLs5152Check dependency manifests for services that typically require connection URLs:5354| Dependency | Expected env var |55|-----------|-----------------|56| `pg` / `sequelize` / `prisma` / `typeorm` | `DATABASE_URL` |57| `mongoose` / `mongodb` | `MONGODB_URI` |58| `ioredis` / `redis` | `REDIS_URL` |59| `@aws-sdk/*` | `AWS_ACCESS_KEY_ID`, `AWS_SECRET_ACCESS_KEY`, `AWS_REGION` |60| `stripe` | `STRIPE_SECRET_KEY`, `STRIPE_WEBHOOK_SECRET` |61| `@sendgrid/mail` | `SENDGRID_API_KEY` |62| `nodemailer` | `SMTP_HOST`, `SMTP_PORT`, `SMTP_USER`, `SMTP_PASS` |63| `@auth0/*` / `next-auth` | `AUTH_SECRET`, `AUTH_URL`, provider-specific keys |6465## Classification6667Classify each detected variable:6869| Category | Examples | Required for deploy? |70|----------|---------|---------------------|71| **Infrastructure** | `DATABASE_URL`, `REDIS_URL`, `PORT` | Yes |72| **Secrets** | `API_KEY`, `SECRET_KEY`, `JWT_SECRET` | Yes |73| **Service URLs** | `NEXT_PUBLIC_API_URL`, `WEBHOOK_URL` | Yes (but values differ per environment) |74| **Build-time** | `NEXT_PUBLIC_*`, `VITE_*` | Yes (must be set during build) |75| **Optional/Debug** | `LOG_LEVEL`, `DEBUG`, `NODE_ENV` | No (has sensible defaults) |7677## Build-time vs runtime7879This distinction matters for Dockerfiles:8081- **Build-time**: Set as `ARG` in Dockerfile, passed via `--build-arg` or `args:` in compose. Includes `NEXT_PUBLIC_*`, `VITE_*`, and any var used during `npm run build`.82- **Runtime**: Set as `ENV` in Dockerfile or `environment:` in compose. Includes `DATABASE_URL`, `PORT`, API keys.8384## Output format8586After detection, report:87881. List of all detected env vars with their source (`.env.example`, source code, framework config)892. Classification (infrastructure, secret, service URL, build-time, optional)903. Which vars are missing values (need user input)914. Which vars have safe defaults (e.g. `PORT=3000`, `NODE_ENV=production`)925. Which vars are build-time and must be in Dockerfile `ARG` directives9394## Related Skills9596- **`pre-deploy-checklist`** — Uses env detection results to validate deployment readiness97- **`dockerfile-generation`** — Build-time env vars identified here need `ARG` directives in the Dockerfile
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