How do I test a Hotwire Native app against a local dev server?

Change the URL in the shell to your machine's LAN address, such as http://192.168.1.20:3000. An iOS simulator can reach localhost but a physical device cannot, because localhost on the phone is the phone. Both platforms also block plain HTTP by default, so development needs an explicit exception.

Find the address and bind to it

ipconfig getifaddr en0
bin/rails server -b 0.0.0.0

The bind flag is the step people miss. By default Rails listens on loopback only, so the phone's request never arrives even with the right address. bin/dev runs the same server, and the same flag applies.

The two platform rules

iOS blocks non-HTTPS requests under App Transport Security. The simulator is more permissive than a device, which is why a build that works in the simulator fails on a phone.

Android blocks cleartext traffic by default from API 28 onward, with a similar result.

Both need a development-only exception in the shell's configuration, under mobile/ios or mobile/android depending on the platform. Add it deliberately and remove it before you submit, because shipping an app that permits cleartext is both a security problem and something review may flag.

The alternative that avoids all of it

Run a tunnel and use HTTPS:

bin/dev

Then expose it with whichever tunnel you use and point the shell at the public HTTPS URL. No transport exceptions, no LAN addressing, and it works from a device on cellular. Worth it if you test on hardware often.

Same network, actually

Phone and laptop on the same Wi-Fi, and a network that does not isolate clients. Guest networks frequently do, and the symptom is a request that simply times out with nothing in the Rails log. Nothing in the Rails log means the request never arrived, which is a network problem rather than an app problem.

Remember APP_HOST

Mailers and canonical URLs read Rails.application.config.x.app_host rather than the request. On a LAN address they will point somewhere the phone cannot follow, which is fine for development and worth knowing when a sign-in link in the app does not work.