Not related to the new assert signatures feature (which is great!), but IMO the two best approaches to do what you want today are: - io-ts[1] This requires yo

Not related to the new assert signatures feature (which is great!), but IMO the two best approaches to do what you want today are: - io-ts[1] This requires you to write your types as a runtime value, and allows you to extract static types from those, e.g.: const ContactInfo = t.type({ address_1: t.string, ... }) type ContactInfo = t.TypeOf<typeof ContactInfo> You can validate objects with `ContactInfo.decode(someObject)` Note that we can have the same name for the type and value because they live in different namespaces. When you do ContactInfo.decode, you're calling the decode property of `const ContactInfo`. When you use `ContactInfo` in a type position (e.g. `function x(arg: ContactInfo)`), you're using the `type ContactInfo` declaration - typescript-is[2] This uses TypeScript's transformer API. You can use it with https://github.com/cevek/ttypescript https://github.com/cevek/ttypescript. It generates validators for your interfaces/types/etc at compile-time. [1]: https://github.com/gcanti/io-ts https://github.com/gcanti/io-ts [2]: https://github.com/woutervh-/typescript-is https://github.com/woutervh-/typescript-is