What is the role of 「の」 particle in the sentence 「何見てるのよ 」


Recently I saw the sentence「何見てるのよ」in manga. It was said by a female
character. I suppose it's translated as "What are you looking at?". But I am
not sure about the role of 「の」in this sentence. So there are 2 questions:

  1. Is 何見てるよ (without 「の」) still a valid sentence and means the same?
  2. What 「の」particle means in this sentence?

Also I've just found, that a 「の」particle can be used by feminine speakers as a
sentence ending particle for emphasizing or questioning tone (which makes
sense in the context of my question). But I am still not sure.




Technically, this の is **not a particle** but a special noun known as
**explanatory-の**. If you aren't familiar with this yet, you have to learn it
first. Although there is no direct equivalent in English, this is very
important when you want to speak Japanese naturally.

  * [What is the meaning of ～んです/～のだ/etc?](https://japanese.stackexchange.com/q/5398/5010)
  * [Explanatory のだ （んだ）](https://www.wasabi-jpn.com/japanese-grammar/explanatory-noda/)

When this type of の appears in a question, it seeks clarification (or
explanation, excuse, etc). You need to use this type of の every time you make
a question about what's already going on now.

  * [Question Markers: か and の](https://www.wasabi-jpn.com/japanese-grammar/question-markers/)

> The connotation that the の has is to seek clarification based on background
> contexts, while the か doesn’t require any context.

何見てるよ is incorrect because it doesn't even look like a question.

In speech, の is very often used with various sentence-end particles, so you'll
see variations like のさ, んだぜ, のよ, んだわ, and so on. It is true that "bare の" is
relatively specific to feminine or childlike speakers in fiction, but other
types of speakers do use explanatory-の as part of more complex sentence
endings. For example, in a situation where a small girl might say 犬が好きなの,
other characters might say 犬が好きな **の** よ, 犬が好きな **ん** だ, 犬が好きな **ん** です, 犬が好きな
**の** さ, and so on. These all translate to "(It's that) I like dogs".




Grammatically [の](https://dictionary.goo.ne.jp/word/%E3%81%AE/#jn-171157) here
is a question marker, #2 (I included #1 as reference):

> １ （下降調のイントネーションを伴って）断定の言い方を和らげる意を表す。多く、女性が使用する。「伺いたいことがある―」「あいにく母は留守です―」
>
> ２ （上昇調のイントネーションを伴って）質問または疑問の意を表す。「君は行かない―」「そんなに悲しい―」「なぜな―」

and [よ](https://dictionary.goo.ne.jp/word/%E3%82%88/#jn-226011) is

> ３ （疑問を表す語に付いて）相手をなじる意を表す。「しゃべったのはだれ―」「何―、この子は」

So, 何見てるの is neutral _what are you looking at_ and よ adds a blaming tone to
it; 何見てるよ is not correct.

* * *

You can search のよ on this site to see other examples. The ending is generally
feminine. A masculine version of the sentence is 何見てんだ(よ).

