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Envalid is a small library for validating and accessing environment variables in Node.js (v6.0 or later) programs, aiming to:

  • ensure that your program only runs when all of its environment dependencies are met
  • give you executable documentation about the environment your program expects to run in
  • give you an immutable API for your environment variables, so they don't change from under you while the program is running


envalid.cleanEnv(environment, validators, options)

cleanEnv() returns a sanitized, immutable environment object, and accepts three positional arguments:

  • environment - An object containing your env vars (eg. process.env)
  • validators - An object that specifies the format of required vars.
  • options - An (optional) object, which supports the following keys:
    • strict - (default: false) If true, the output of cleanEnv will only contain the env vars that were specified in the validators argument.
    • reporter - Pass in a function to override the default error handling and console output. See lib/reporter.js for the default implementation.
    • transformer - A function used to transform the cleaned environment object before it is returned from cleanEnv
    • dotEnvPath - (default: '.env') Path to the file that is parsed by dotenv to optionally load more env vars at runtime. Pass null if you want to skip dotenv processing entirely and only load from process.env.

By default, cleanEnv() will log an error message and exit if any required env vars are missing or invalid.

const envalid = require('envalid')
const { str, email, json } = envalid
const env = envalid.cleanEnv(process.env, {
    API_KEY:            str(),
    ADMIN_EMAIL:        email({ default: '' }),
    EMAIL_CONFIG_JSON:  json({ desc: 'Additional email parameters' })
// Read an environment variable, which is validated and cleaned during  
// and/or filtering that you specified with cleanEnv(). 
env.ADMIN_EMAIL     // -> '' 
// Envalid parses NODE_ENV automatically, and provides the following 
// shortcut (boolean) properties for checking its value: 
env.isProduction    // true if NODE_ENV === 'production' 
env.isTest          // true if NODE_ENV === 'test' 
env.isDev           // true if NODE_ENV === 'development' 

For an example you can play with, clone this repo and see the example/ directory.

Validator types

Node's process.env only stores strings, but sometimes you want to retrieve other types (booleans, numbers), or validate that an env var is in a specific format (JSON, url, email address). To these ends, the following validation functions are available:

  • str() - Passes string values through, will ensure an value is present unless a default value is given. Note that an empty string is considered a valid value - if this is undesirable you can easily create your own validator (see below)
  • bool() - Parses env var strings "0", "1", "true", "false", "t", "f" into booleans
  • num() - Parses an env var (eg. "42", "0.23", "1e5") into a Number
  • email() - Ensures an env var is an email address
  • url() - Ensures an env var is a url with a protocol and hostname
  • json() - Parses an env var with JSON.parse

Each validation function accepts an (optional) object with the following attributes:

  • choices - An Array that lists the admissable parsed values for the env var.
  • default - A fallback value, which will be used if the env var wasn't specified. Providing a default effectively makes the env var optional.
  • devDefault - A fallback value to use only when NODE_ENV is not 'production'. This is handy for env vars that are required for production environments, but optional for development and testing.
  • desc - A string that describes the env var.
  • example - An example value for the env var.
  • docs - A url that leads to more detailed documentation about the env var.

Custom validators

You can easily create your own validator functions with envalid.makeValidator(). It takes a function as its only parameter, and should either return a cleaned value, or throw if the input is unacceptable:

const { makeValidator, cleanEnv } = require('envalid')
const twochars = makeValidator(x => {
    if (/^[A-Za-z]{2}$/.test(x)) return x.toUpperCase()
    else throw new Error('Expected two letters')
const env = cleanEnv(process.env, {
    INITIALS: twochars()

You can, and should, also provide a type with your validator. This can be exposed by tools to help other developers better understand you configuration options.

To add it, pass a string with the name as the second argument to makeValidator.

const { makeValidator } = require('envalid')
const twochars = makeValidator(x => {
    if (/^[A-Za-z]{2}$/.test(x)) return x.toUpperCase()
    else throw new Error('Expected two letters')
}, 'twochars')

Error Reporting

By default, if any required environment variables are missing or have invalid values, envalid will log a message and call process.exit(1). You can override this behavior by passing in your own function as options.reporter. For example:

const env = cleanEnv(process.env, myValidators, {
    reporter: ({ errors, env }) => {
        emailSiteAdmins('Invalid env vars: ' + Object.keys(errors))

.env File Support

Envalid wraps the very handy dotenv package, so if you have a .env file in your project, envalid will read and validate the env vars from that file as well.

Usage within React Native

Envalid can be used within React Native with a custom reporter. Also the usage of dotenv must be disabled by setting options.dotEnvPath to null.

Instead of dotenv react-native-config can be used to read the configuration.


const reactNativeConfig = require('react-native-config')
const rawConfig = reactNativeConfig.default
const validatedConfig = envalid.cleanEnv(
    // validators 
    dotEnvPath: null,
    reporter: ({ errors = {}, env = {} }) => {
      // handle errors 



A helper function called testOnly is available, in case you need an default env var only when NODE_ENV=test. It should be used along with devDefault, for example:

const env = cleanEnv(process.env), {
  SOME_VAR: envalid.str({devDefault: testOnly('myTestValue')}),

For more context see this issue.