What is the ruling on chatting online during Ramadan?

Chatting between a man and a non-mahram woman is not permissible, as it is a means to corruption, whether in Ramadan or otherwise. As for chatting between a man and a man, or a woman and a woman, if it involves beneficial conversation free from obscenity and flirtation, then there is no harm in it. However, it is generally better to avoid it due to the time wastage involved, especially in Ramadan, because utilizing time for what is beneficial is superior.