env-detection

DevOps & Security

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.

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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 readiness
dockerfile-generation — Build-time env vars identified here need ARG directives in the Dockerfile