Yes, tag what you see, and don't tag subjectively.

Speaking hypothetically:
I see a male with androgynous features (female traits in this case), which typically results in them being tagged as newhalf (or whatever else might fit).


How would one go about tagging gender in this case? 1boy, 1girl, or none at all?

Normally I'd just tag as 1boy, androgynous and be done with it, because regardless of how you look at it, they are biologically males.
But now I'm not so sure as there are anons tag-fighting, insisting that newhalfs are women, because "that's what they define themselves as" and "according to law they are X gender". Would cases like these be exceptions?

Thanks in advance.

First off, the laws of any given country do not apply to tagging. i.e. having consensual (informed or otherwise) sex with a minor is statutory rape in the USA but we do not use the rape tag for consensual sex even if it's with a minor. We also do not care about the feelings of certain SJWs here.

Because we get a significant number of posts and tags from Danbooru, around a year ago the trap tag had to be redefined to coincide with Danbooru's policy of tagging males of feminine appearance as oto no ko, retagged as trap on Gelbooru. Traps are male for tagging purposes and get the #boy tags. Futanari and newhalf are their own genders and do not get #boy or #girl tags.

For genuinely androgynous characters with male genitals it may be best to simply not use #boy tags. This is most likely to happen with young characters without secondary sex character traits. Most artist draw shota and loli different enough to tell the difference. A tight belly, straight hips and "hart-shaped" butt are usually male traps while a flat-chested newhalf might have a "Squid-belly", wide hips and more developed glutial fold or thigh-gap. Again, if you really can't tell the difference then just leave the gender tags off.

Ah I see, thank you for clarifying.

Incorrect. Female-bodied futanari in particular always gets female counter tags. Futanari being its own gender doesn't really matter here; the counter tags are based on body type rather than actual sex, so the actual genitals are usually ignored. The exception to this is traps, who should always receive male counter tags. The majority of newhalf characters have a completely female body type, so you would usually tag them using female counter tags. An exception comes up if they identify as male, in which case they are also a trap and should be tagged as such. This is fairly uncommon, though.

You might have been thinking of the orientation tags, which are based on actual biological sex and don't apply to futanari. They do sorta apply for newhalf. I'm not really exact on the details myself, so I usually just leave it alone unless the newhalf qualifies as a trap.

Futa = girl
Newhalf = girl & futa_with_male/female/futa (if not solo).

Also, it doesn't make sense to automatically tag every trap with "androgynous", since trap means to pass as a girl.