JSON to TypeScript interfaces: use generated types without lying to yourself

Paste JSON into a generator and you get a pleasing interface in seconds. That speed is useful, as long as you remember the generated type is inferred from one sample and TypeScript erases it at runtime.

Short answer: generate types to remove mechanical typing, then review nullable fields, arrays, IDs, timestamps, and unions. Validate untrusted JSON at the boundary; an interface cannot stop an API from returning the wrong shape.

interface Order {
  id: string;
  totalCents: number;
  createdAt: string; // parse as a date at the boundary
  items: Array<{ sku: string; quantity: number }>;
}

as Order is a type assertion, not validation. It tells the compiler to trust you; it does not inspect one byte of JSON.

Start with the JSON to TypeScript generator, then put a schema validator at the network boundary and map the external payload to your internal model. Generated types are scaffolding, not a contract.

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