In case you receive the following message

"Sorry internet hipster, this little side project requires JavaScript."

here is a quick example of how to get the pages the "traditional way"[FN1]:

     #/bin/sh
     test $# -eq 2||exec echo usage: $0 source target;

     exec curl -H"Content-type: application/json" \
     -d '{"source":"'$1'","target":"'$2'"}' \
     https://api.sixdegreesofwikipedia.com/paths \
     |exec sed '
     s/\",/\"\
     /g;s/,\"/\
     \"/g;s/:{/:\
     {/g;s/}/&\
     /g;s/\"pages\":/&\
     /'

It appears the author is using the Wikipedia API. I did not add any HTML tags, etc. to the output, although this is very easy to do.

FN1. The original "web browsers" needed no GUI, no Javascript.