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Environment Variables

The table below lays out environment variables for the Lexicon Mobile App.

If there is a default value indicated, you do not need to set it.

Environment VariableRequiredNotesDefault ValueExample Value
MOBILE_PROSE_HOSTYesThe hostname of the Prose Server (must start with http or https)-
MOBILE_PROSE_PORTNoThe port of the Prose Server(empty)8080


Note that MOBILE_PROSE_HOST must always be specified, and must always start with either http:// or https://.

Otherwise The Lexicon Mobile App has no idea what server to talk to in order to interact with Discourse.

Different Behavior in Development

If the Mobile App detects that NODE_ENV is not production, then it will adjust its behavior slightly if MOBILE_PROSE_HOST is making use of localhost or

In this case, a replacement will be made using Expo's debuggerHost constant, which is used to locate the IP address of your development machine.

This addresses multiple issues:

  • Accessing localhost from within the Android simulator does not map to your development machine
  • Accessing localhost from a device running Expo Go does not map to your development machine, requiring you to manually identify and specify your development machine's IP address with MOBILE_PROSE_HOST.

If you are interested in more details about this, the implementation of this behavior is available in frontend/constants/app.ts.


MOBILE_PROSE_PORT is used to allow explicitly specifying the port number.


If it is not set, only MOBILE_PROSE_HOST will be used to derive the host of the Prose

This presents a situation where you could omit MOBILE_PROSE_PORT and still specify a port number, if you desired: