The command jekyll server, by default, binds to 127.0.0.1, as you can see in the following logs.

$ jekyll serve
[...]
Server address: http://127.0.0.1:4000/
Server running... press ctrl-c to stop.

This means that the website is only accessible by the device that you are running the command.

To make the website accessible by other devices on the same network, run jekyll serve --host=0.0.0.0.

$ jekyll serve --host=0.0.0.0
[...]
Server address: http://0.0.0.0:4000/
Server running... press ctrl-c to stop. 

This will make the Jekyll blog accessible by the IP address of your machine, and thus accessible by other devices on the same network.

A neat command that you can use to find the IP address of your machine is the following:

ifconfig en0 | grep "inet " | awk '{print $2}'

This will output your IP on the Terminal in the format 192.168.0.XXX.

Type this IP followed by :4000 on your favorite browser and you will be able to now browse your blog from the mobile device!! :rocket: