"It worths it", "it worth it" or "it is worth it"?

Which one is correct and why?

I think "worth it" is an adjective phrase. So what is "worth" then?

Example:

You should try spending money on her. It worths it.

You should try spending money on her. It worth it.

You should try spending money on her. It is worth it.

Which one is right? The last 2 are not condemned by grammar checker.

Worth as a verb is obsolete. Where have you seen or heard It worths it or It worth it?

What you will find is It’s worth it, used to describe something that has a value equivalent to what is being asked for it either in terms of money or effort. In that use, worth is an adjective.

Only the last one is correct.

"Worth" is classified as an Adjective and used as one. (Although it also acts differently from all of the Adjectives.)

In your particular example, "worth" is used as an Adjective but acts as a Preposition. That's why it's normally followed by a Noun, a Pronoun or a Gerund.

Ex.

It's worth a try.

It's worth it.

It's worth trying.