There are lots of other good validation libraries for Node (zod, joi, class validator) but they didn't hit the development sweet spot for me.

This TypeScript-only library gives you: (1) Class-based schemas that serialize and deserialize (2) Static types by default without an additional infer call (3) Custom validation by adding methods to a schema class (4) Simple way to access additional context (eg the request object) when parsing (5) An API broadly similar to OpenAPI and JSON Schema