SageMath is a free open-source mathematics software system. You can use a SageMath cell online by going here.
diff(f,x)
--- derivative of with respect to xvar("x,y")
f = x*exp(-3*y) + sin(2*x-5*y)
diff(f,x)
diff(f,x,y,x)
--- xxxxxxxxxx
var("x,y")
f = x*exp(-3*y) + sin(2*x-5*y)
diff(f,x,y,x)