There is Duckduckgo Bangs - https://duckduckgo.com/bangs. They directly searches inside a website. There are a total of 13,563 bangs of websites. Twitter, Amazon, Stackoverflow, wikipedia, arch linux. You have to set your search engine to DDG though.

Wanna check if Thunderbird v115 is in arch repos? Ctrl + L, !archpkg thunderbird

Boom!

My favourites:

!w <term> searches <term> inside Wikipedia

!so <term> searches for that term inside stackoverflow

!a <term> searches inside amazon.com

!ai <term> searches inside amazon.in

!arch <term> searches inside arch wiki article for that term

!archpkg <term> directly searches for archlinux.org/packages

Also, I just learned that there is a "!hackernews"