TypeScript provides, primarily, a type verification system. JSON-schema provides a type assertion system. Both serve as type documentation systems. TS says "

TypeScript provides, primarily, a type verification system. JSON-schema provides a type assertion system. Both serve as type documentation systems. TS says "if you create objects in my world, I will use my type system to verify that you're creating the right kind of objects, and you can look up their definitions to see what's in them". JSON-schema says "if you give me external, un-annotated objects, I can tell you whether they comply with a type definition, and you can look at that definition to see what's in them". TS has a limited assertion facility, but it's not nearly as capable as JSON-schema. Projects like io-ts (https://github.com/gcanti/io-ts https://github.com/gcanti/io-ts) add more functionality to those assertions, but they're still much less easy to use, in my opinion, than JSON-schema for this purpose. If you're using TS types to assert, though, you can definitely describe more complex constraints, so it may make sense as an alternative to JSON-schema for some people. As others have pointed out, JSON-schema is also much easier to use on non-TypeScript platforms than TS assertions, which, even if you use an assertion library like io-ts, will still be limited in use to JavaScript (and JS-to-$other_language runtimes).