Zod Validation Guide for TypeScript
Zod is the most popular TypeScript-first schema validation library with 90M+ weekly npm downloads. This guide covers everything from basic schemas to advanced patterns used in production TypeScript applications.
JSON to Zod Converter
Convert JSON or JSON Schema to Zod validation schemas. Supports $ref, allOf/oneOf/anyOf, enum, format constraints, and nested objects.
About JSON to Zod Converter
- Two input modes — paste raw JSON data to infer schemas, or paste a JSON Schema for precise conversion with
$ref,allOf/oneOf/anyOf, and constraints. - JSON Schema support — converts
required,enum,const,format(email, uri, uuid, date-time, ipv4, ipv6),pattern,minimum/maximum,minLength/maxLength,default, and$defs/definitions. - Smart inference — detects emails, URLs, UUIDs, and ISO dates in raw JSON values and adds appropriate Zod refinements.
- Required vs optional — JSON Schema
requiredarrays map to required fields; all others get.optional(). - TypeScript type — generates
z.infer<typeof schema>so you get TypeScript types for free. - Everything runs in your browser — no data is sent over the network.
Why Zod dominates TypeScript validation
Zod solves a fundamental TypeScript problem: TypeScript types exist only at compile time and are erased at runtime. Zod schemas validate data at runtime AND infer TypeScript types via z.infer<typeof schema>, giving you a single source of truth. This eliminates the common bug where your TypeScript interface says a field is a string but the API actually returns null. Zod catches this at runtime instead of crashing in production.
Common Zod patterns
z.string().email() validates email format. z.number().int().positive() ensures positive integers. z.enum(['admin', 'user', 'viewer']) creates a union of literal types. z.object({}).strict() rejects unknown keys. z.array(z.string()).min(1) requires at least one item. z.union([z.string(), z.number()]) accepts either type. z.discriminatedUnion('type', [...]) efficiently validates tagged unions. These patterns cover 90% of real-world validation needs.
Zod with React Hook Form, tRPC, and Next.js
Zod integrates deeply with the TypeScript ecosystem. With React Hook Form, use @hookform/resolvers/zod to get automatic form validation with type-safe error messages. With tRPC, Zod schemas define your API input/output types and validate them automatically. With Next.js Server Actions, Zod validates form submissions on the server. These integrations mean your Zod schemas become the contract between your frontend and backend.
Frequently Asked Questions
Is Zod better than Yup or Joi for TypeScript?
For TypeScript projects, Zod is generally the best choice. Unlike Yup and Joi, Zod was built from scratch for TypeScript with first-class type inference via z.infer. Yup's TypeScript support was retrofitted and has edge cases where inferred types are incorrect. Joi has no official TypeScript type inference at all.
How do I use Zod with React Hook Form?
Install @hookform/resolvers, then pass your Zod schema to useForm: useForm({ resolver: zodResolver(mySchema) }). Form errors will automatically match your Zod validation messages, and the form data type is inferred from the schema.
Does Zod work at runtime or only at compile time?
Both. Zod validates data at runtime (schema.parse(data) throws if invalid, schema.safeParse(data) returns a result object). It also infers TypeScript types at compile time via z.infer<typeof schema>. This dual behavior is Zod's key advantage.
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