Genuine, honest, and sincere are the antonyms for the phrase "puts on a false front." When someone puts on a false front, they pretend to be someone or something they're not. They might use fake charm, feigned interests, and even lies to mislead others. Conversely, when someone is genuine, they are truthful, transparent, and authentic. They do not need to hide behind a façade of lies or act in any way other than their true selves. Honesty and sincerity are synonymous with being genuine, and they promote trust and credibility between individuals. In short, putting on a fake front might help in the short-term, but it will ultimately harm any relationship or interaction in the long run.