Fay looks neat! I'll have to play with it. Since the whole rules language is custom, we're not using any off-the-shelf projects presently, and to be honest, w

Fay looks neat! I'll have to play with it. Since the whole rules language is custom, we're not using any off-the-shelf projects presently, and to be honest, we've only scratched the surface of what's possible. Most of what we have in place right now is at the level of type-checking and other expression-correctness checks (we're intentionally more strict about a number of things than JavaScript). But given the nature of the rules we can do a lot of cooler analysis, like detect redundant or conflicting rules. We should also be able to do interesting analysis for the developer like answer questions like "What parts of my Firebase data can an unauthenticated client read or write?", "What parts can a user authenticated as 'joe' read or write?" This sort of analysis should help developers reason about their rules and verify their correctness. Honestly, I'm pretty excited about the possibilities. :-)