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LoopBack applications have the following types of configuration files:

  • Application-wide configuration files, by default server/config.json. You can also use server/config.local.js to set values that you can’t with simple JSON.
  • Data source configuration files, by default server/datasources.json. You can also use server/datasources.local.js to set values that you can’t with simple JSON.
  • Application-level configuration of Models, by default server/model-config.json.
  • Middleware configuration files, by default server/middleware.json.
  • Configuration files for LoopBack components, by default server/component-config.json.

LoopBack will always load the following configuration files, if they exist:

  • server/config.json.
  • server/config.local.json or server/config.local.js
  • server/datasources.json
  • server/datasources.local.json or server/datasources.local.js
  • server/model-config.json
  • server/model-config.local.json or server/model-config.local.js
  • server/middleware.json
  • server/middleware.local.json or server/middleware.local.js
  • server/component-config.json
  • server/component-config.local.json or server/component-config.local.js

Additionally, when the NODE_ENV environment variable is set, LoopBack will load configuration from:

  • server/config.env.json/js
  • server/datasources.env.json/js
  • server/model-config.env.json/js
  • server/middleware.env.json/js
  • server/component-config.env.json/js

where env is the value of NODE_ENV (typically “development,” “staging,” or “production”). This enables you to set up configurations for development, staging, and production environments. 

Examples of the application configuration files:

Examples of data source configuration files:

Examples of the middleware configuration files:

For an example application, see

Application-wide configuration

Define application server-side settings in server/config.json.

You can override values that are set in config.json in:

  • config.local.js or config.local.json
  • config.env.js or config.env.json, where env is the value of NODE_ENV (typically development or production). For example config.production.json.

For example:


module.exports = {
  host: process.env.CUSTOM_HOST,
  port: process.env.CUSTOM_PORT

Ensure stack traces are not returned

By default, stack traces are not returned in JSON responses, but if they were enabled for development and debugging, ensure they are turned off for production.

  • Set the NODE_ENV environment variable to “production”
  • Include the following in server/middleware.production.json:


"final:after": {
    "strong-error-handler": {}

Disabling API Explorer

LoopBack API Explorer is great when you’re developing your application, but for security reasons you may not want to expose it in production.

For an application using loopback-component-explorer, to disable explorer in production:

  • Set the NODE_ENV environment variable to “production”.
  • Then in server/component-config.production.json:


  "loopback-component-explorer": null

Include stack traces in HTTP responses

By default, LoopBack 3.0 applications exclude error stack traces from HTTP responses (typical in production). For development and debugging, you may wish to include them; to do so, set the NODE_ENV environment variable to development so the app will use middleware.development.json.

This file includes the following that will include stack traces in HTTP responses:

  "final:after": {
    "strong-error-handler": {
      "params": {
        "debug": true,
        "log": true

Data source configuration

You can override values set in datasources.json in the following files:

  • datasources.local.js or datasources.local.json
  • datasources.env.js or datasources.env.json, where env is the value of NODE_ENV environment variable (typically development or production). For example, datasources.production.json.

Example data sources:


  db: {
    connector: 'memory'


  db: {
    connector: 'mongodb',
    database: 'myapp',
    user: 'myapp',
    password: 'secret'

You can also configure your datasource.env.js file to use environment variables:


module.exports = {
  db: {
    connector: 'mongodb',
    hostname: process.env.DB_HOST,
    port: process.env.DB_PORT || 27017,
    user: process.env.DB_USER,
    password: process.env.DB_PASSWORD,
    database: 'myapp',

In the above example, running export PRODUCTION=true (or set PRODUCTION=true for Windows) will load the datasource.

Getting values from environment variables

You can easily get the value of an environment variable in an application. The command you use depends on your operating system.

MacOS and Linux

Use this command to set an environment variable and run an application in one command:

$ MY_CUSTOM_VAR="some value" node .

or in separate commands:

$ export MY_CUSTOM_VAR="some value"
$ node .

Then this variable is available to your application as process.env.MY_CUSTOM_VAR.


On Windows systems, use these commands:

C:\> set MY_CUSTOM_VAR="some value"
C:\> node .