The Soft Circuits Toolkit allows anyone to prototype fully soft circuits that work on air instead of electricity. The toolkit aims to interest youth in circuit-building, electronics, and engineering and inspire them to become the engineers of the future. The pneumatic circuits can be used to learn about how circuits work in general, but also to create playful and functional soft devices. Because these designs are fully soft and thus safer for humans to interact with, they show great potential in areas such as healthcare and human-robot interaction. The Soft Circuits Toolkit includes a range of components, including those that you normally find in analogue electronics kits. This allows anyone, but especially youth, to playfully and safely experiment with these pneumatic circuits and create their own soft designs.