In case https://www.rubydoc.info/ Show archive.org snapshot is to slow or offline, you can also read a gem documentation offline.
Start a server with gem server and go to http://0.0.0.0:8808/. Here you will find a list of all installed gems and it is possible to navigate to the documentation if installed e.g. http://0.0.0.0:8808/doc_root/rubocop-0.77.0/
In case you set the configured RubyGems to not install documentation by default, you need to add generate the documentation for the specific gem.
gem install rubocop --document
Known errors
undefined method `path=' for #<WEBrick::HTTPRequest:0x000055eb55fbff90>
Upgrade
Show archive.org snapshot
RDoc with gem update rdoc.
Posted by Arne Hartherz to makandra dev (2011-01-31 15:56)