Infer Types

Zod · Reference cheat sheet

📋 Overview

Zod schemas are a single source of truth: validate at runtime and derive TypeScript types with z.infer, z.input, and z.output.

🔧 Core concepts

💡 Examples

Basic infer:

const User = z.object({
  id: z.string(),
  email: z.string().email(),
});
type User = z.infer<typeof User>;
// { id: string; email: string }

Input vs output:

const S = z.string().transform((s) => s.length);
type In = z.input<typeof S>;   // string
type Out = z.output<typeof S>; // number

Function boundary:

function save(user: z.infer<typeof User>) {
  /* ... */
}

⚠️ Pitfalls

• Don't hand-write a duplicate interface that can drift — infer from the schema.
• Optional fields (?) vs | undefined differ slightly in TS excess property checks.
• Circular types need z.lazy — plain infer won't recurse infinitely by itself.

🔗 Related

• transforms.md
• objects.md
• safeparse.md
• getting_started.md