`json` is a "default gem": https://stdgems.org/ https://stdgems.org/ Meaning Ruby ships with that gem pre-installed, but it's still a gem and you can upgrade/d

`json` is a "default gem": https://stdgems.org/ https://stdgems.org/ Meaning Ruby ships with that gem pre-installed, but it's still a gem and you can upgrade/downgrade it in your gemfile if you so chose. As for `require "json/ext"` that's outdated knowledge.