dotenv

dotenv is the library and convention that loads .env files into environment variables; it is the most popular in the Node.js ecosystem and externalizes configuration.

Purpose

To let local development manage configuration with a .env file while production uses real environment variables, without code changes.

Mechanism

At startup it reads the .env file, parses KEY=VALUE lines, and injects them into process.env. It supports multiple environments (.env.development), variable interpolation ($VAR), and quote handling. It does not override existing environment variables (unless override is set).

Use cases

Local configuration for Node.js projects
Next.js/Vite environment variables
Docker Compose env_file
Test environment isolation

Examples

Input

.env: API_KEY=secret

Output

process.env.API_KEY="secret"

Loaded into the environment

Common errors

Loading dotenv in production wastes startup time: Use real environment variables in production and do not load .env

Related terms

An ENV file defines environment variables in KEY=VALUE format for application configuration; it is the recommended approach of 12-factor apps.

INI is a traditional configuration file format that groups settings with [section] headers and key=value pairs; it is simple but unstandardized, and implementations differ slightly.

Java Properties files use KEY=VALUE or KEY:VALUE format; they are the traditional configuration format of the Java ecosystem and support Unicode escapes.

Related tools

Parse .env-style KEY=VALUE lines into JSON. Blank lines and #-prefixed comments are skipped. dotenv conventions beyond that are not implemented: an "export " prefix stays in the key (export PORT=3000 → "export PORT"), and quotes around values are kept verbatim.

ENV Stringify — pure client-side tool. Privacy-first, no server round-trip.

Json To Env — pure client-side tool. Privacy-first, no server round-trip.

Yaml To Env — pure client-side tool. Privacy-first, no server round-trip.

References