I'm not sure about you but I always enjoy dealing with people who are direct, say what they mean, and don't hide behind facades — even if their hard truths can sometimes be hard to swallow.
In both my personal or professional life, I often find it more productive interacting with people who have no qualms about openly expressing how they feel.
In both Spanish and English, such wonderful people are described the same way: ‘cómo un libro abierto’ or ‘like an open book’.
Alternatively, depending on the context, you could also use the following:
Eg. Juan is so transparent you can count on him to always be honest with you.
→ Easy to read = que está claro lo que piensa una persona, aunque no tiene que ser porque lo muestra, también podría ser porque no lo esconde bien.
Eg. Juan is extremely easy to read. It wouldn’t serve him well to try and hide how he really feels about the direction the company is heading.
I hope that helps!
Soy el director de Daniel Smith + Partners. Tengo más de 15 años de experiencia enseñando inglés a españoles.