The only part that made me comment was the rules definitions. I will gladly write key/value type config in JSON or YAML or whatever. But, writing the rules logi

The only part that made me comment was the rules definitions. I will gladly write key/value type config in JSON or YAML or whatever. But, writing the rules logic in it would be a big pain, because it is not easy to see what deeply nested and and or statements mean. JSON is definitely nice for the time vs. effort balance; you've effectively got the users writing AST directly. And, building tooling to make it easier to write and manage is good. I've had a couple of projects recently where I was writing a parser. And, there is a lot of tooling to make it easier: lex/flex, yacc/bison, PEG-style tools like Python's Parsimonious [0]. (I'm sure there are similar libraries in JavaScript) Defining the grammar is a bit arcane, but the only other thing you write is the interpreter, which you already have a version of (just with a different AST format). In any case, the project/service is really cool! [0] https://github.com/erikrose/parsimonious https://github.com/erikrose/parsimonious