On screen chemistry-Writers' creation or actors' improvisation?

Good director can motivate and squeeze out what he wants from the actors but actors should also be that much receptive and respond to what the director says :)

Actors ... its something effortless and natural, the same actors in different films with totally different script and director still have the same blazing chemistry.

Chemistry is a natural affinity, a spark between 2 actors which translates into onscreen chemistry

And yes, chemistry can be platonic...best example being SRK-Kajol who have a genuine friendship and understanding in real life which translates into chemistry onscreen

I think it's the actors who should get most credit for it. But, the writing also plays a part, although a smaller one. I read this somewhere, and it may be true in the cases of established jodis which can't recreate their magic too, that real-life couples often take their romance for granted, they probably get too complacent or too conscious and then can't create the tension onscreen which is there in real life. Same probably for couples who have had great chemistry in previous films, they probably become overconfident about this and lose it in the next one.

A writer can definitely help because they can create such scenes where the actors would inevitably show some tension but overall, I think it's the actors who really understand the scene well and try to make it as real as possible, which makes it magical.