Need some advice. Recently met a girl the the local gym, and while she and I didn't really talk that much during the initial few months, I feel that things have escalated rather quickly in the past month or so and there's frequent mutual teasing involved with giggles and smiles. How do I know if she's just being friendly or flirty? I also don't want to unintentionally only give off 'friendly' vibes but also communicate my interest in her via flirty teasing so I'd need to know the difference between the two. Any advice appreciated. Open to providing more details if need be.

Edit: Thanks for all the advice guys! A lot of you have advised me to ask her out, but as of now, I really want to make sure that the attraction is mutual, if there even is any from her side before making a move. I really appreciate your time and effort for encouraging me. Thanks once again!