"what are you doing tonight ?" and“ what are you up to tonight?” are these different?

Question

"what are you doing  tonight  ?" and“  what are you up to tonight?”  are  these different?

Answer

The meaning is the same. The only difference is 'what are you up to tonight' is more casual. I wouldn't for example say this to my boss.

Answer

They're the same :)
2nd is a little more casual/informal

Answer

"What are you doing tonight?" is the more formal of the two.  However, the second one can also imply that you are going to do something "no good" or naughty.