I've been thinking a lot about libraries, and single-header-files, and APIs, and I really need a hobby. I have an idea for a new kind of library, and am implementing it for a simple JSON parser because: there isn't a simple stb style parser, and its a small problem that is easy to test.
While this is not exactly stb-style single header library, but jsmn is really good json tokenizer as two file library (h + c file). It's fast, super simply API and it does 0 memory allocations. I used it for my TwitchNotify.