Just to add a slightly different perspective: I'm comfortable with the notation and calculus involved, but had not known how backpropagation worked until now.

Just to add a slightly different perspective: I'm comfortable with the notation and calculus involved, but had not known how backpropagation worked until now. I'm not sure if it's the same for others, but I don't find bare text descriptions with formulas particularly useful. Mathematical notation on a page is great for rote application of rules and computation, but by itself does not easily communicate an intuitive understanding of the system the math represents. I have to work very hard to build up mental pictures of systems described by just notation, and those mental pictures often have to move in complicated ways as well. The relationship between maths on the page and the systems they describe is the same as seeing musical notation on a page and hearing a full orchestra. One is a dry accounting of the facts involved. The other is moving and powerful in its richness and immediacy, a living thing that defies easy communication beyond the experience itself. Demonstrations like this show you the maths _and_ build up a picture for you at the same time. The result of that is that you can communicate a very powerful idea (e.g. backpropagation) very precisely, intuitively and quickly. Very much worth a five minute scroll for me; YMMV!