【～が要る】 Is 要る an adjective? Why not を？

Question

「要る」をneedと訳してしまうと、どうして「～を要る」にならないのか、わかりません。

Answer 1

要る is an intransitive verb that means "to be necessary" or "to be needed" rather than "to need". (No i-adjective ends with る in Japanese.) That's why we mark the needed thing using が rather than を. For example, the very literal translation of お金が要る is "Money is needed", but in English, it's usually more natural to translate this as "[I] need money". Likewise, "要る?" is usually translated as "Do you want/need it?", but its literal translation is "Is it necessary?".

(The link by Chocolate explains a rather exceptional case where 要る is used as part of the AをBと + verb pattern, but this doesn't mean 要る can take を alone.)