A typing test can tell you your words per minute and overall accuracy. But those two numbers leave a useful question unanswered: which keys should you practise next?

I'm Vivek Gupta, the creator of NinjaType , a free, open-source typing practice app. It combines typing tests with focused finger lessons, per-key feedback, and ways to make practice more engaging.

For fellow developers, here's a look at the learning experience and the implementation choices behind it.

Start with two keys, then expand

A large catalogue of drills can make it hard to choose where to start. NinjaType keeps the finger curriculum compact: four finger pairs, with three cumulative levels each.

The index-finger path starts with just F and J . Level two adds G, H, R, U, T, and Y; level three adds V, B, N, and M.…