Even if your entire stack is TS, you still need validation because the submitted data from an external interface (API call) might not be valid.
You can't just accept any JSON payload and expect it to be valid.
In Java or .NET, it will fail at serialization when the runtime tries to map it to a static type (automatic). This is not the case at runtime with JS (because at runtime, it's no longer TS). Thus you need a Zod or a Valibot to ensure the incoming payload is actually valid by describing the valid types (even if your whole stack is TS at dev time because schema mismatches are a runtime problem).
.NETs System.Text.Json does the mapping and validation using either reflection or AOT generated serializers transparently and automatically because it has static types.
You can't just accept any JSON payload and expect it to be valid.
In Java or .NET, it will fail at serialization when the runtime tries to map it to a static type (automatic). This is not the case at runtime with JS (because at runtime, it's no longer TS). Thus you need a Zod or a Valibot to ensure the incoming payload is actually valid by describing the valid types (even if your whole stack is TS at dev time because schema mismatches are a runtime problem).
.NETs System.Text.Json does the mapping and validation using either reflection or AOT generated serializers transparently and automatically because it has static types.