It actually learns

After getting XOR working, I tried my neural net on MNIST (handwritten digit recognition). Loading the data was easier than expected, though getting it into the right shape for my network took some fiddling. To make sure I loaded it correctly, I drew a few of the digits to check they looked right before training.

Once that was sorted, training worked well, and the results were better than I hoped: 97.8% accuracy, in about 5 minutes.

I also experimented with running the whole thing in a browser, but that turned out to be more involved than expected, so I’m parking it for now and focusing on other improvements first.