how to know if hot springs are mixed

ok how do you know if a hot spring is co-ed (male and female are both aloud in the bath)
and how do you know only male or female are just alowd.

I also need to know how to know on the hotel web site because i don't understand how the put it on the websites.

Any responsible guide book will mention if a bath is mixed. As a general rule, they are not mixed, especially not in case of ryokan. If a ryokan does not mention a mixed bath, you can assume that their baths are gender separated.

And last but not least, there should be explanations and instructions at the bath itself. Since these might not be available in English, I recommend to inform yourself in advance about the bath you are intending to visit.

If you see ����(read kon-yoku), then it is mixed but it is extremely rare & only in remote areas. Or the water is too opaque naturally to see under water. Even if konyoku onsens, they generally have gender separated onsen baths, too. So you don't have to worry about it unless you are looking for one.

Konyoku baths are probably less than 1% of the onsen in Japan- the chances of you coming across one without planning to are pretty low, especially with a ryokan.