Sketch the derivative of a function by hand and watch it graded live, then flip the problem and build a valid antiderivative.
Phase one shows f(x); you drag across the lower graph to sketch its derivative, with sign, zeros and concavity scored against the exact answer in real time. Phase two shows a derivative g(x); you pick which antiderivative family fits and set the +C offset so its slope matches g.
Slopecraft links a function to its derivative and back, building the core intuition of calculus.
Sketching the derivative of a displayed function, scored on sign, zeros and concavity, is graphical differentiation.
Grading those three features rather than the exact curve is the original scoring.
They are the right three because they are the qualitative content. Where the function rises the derivative is positive, at a turning point it is zero, and the function's concavity is the derivative's own slope — which is the whole relationship, reachable without computing anything.
Slopecraft is an original free browser calculus game that links a function to its derivative and back again, building visual intuition for slope, concavity and the constant of integration.