Schema definition, parse vs safeParse, transforms, coerce, ZodError.

Zod — Runtime Schema Validation with TypeScript Integration

Zod is a TypeScript-first schema validation library. Schemas are both validation rules and type inferrers: z.infer<typeof schema> extracts the TypeScript type. parse() throws ZodError on failure; safeParse() returns {success, data, error}. Transform and refine add custom logic. Coerce auto-converts types (string → number from form inputs). Zod integrates with react-hook-form, trpc, and drizzle for end-to-end type safety.

Interactive Pipeline Flow

UnderstandImplementOptimise

📐 Define — z.object({...})

Define schema: const userSchema = z.object({ name: z.string().min(1), age: z.number().int().positive(), email: z.string().email() })

Architecture Diagrams

End-to-end type safety with tRPC and Zod.

Loading diagram...

Key Design Decisions

🧠z.infer is the key to single-source-of-truth types

Don't write a TypeScript interface AND a Zod schema separately. Define the Zod schema once, derive the type with z.infer<typeof schema>. Changes to the schema automatically update the type.

🛡️Use safeParse everywhere in web handlers

parse() throws on invalid input — in async Express/Fastify handlers, uncaught throws crash the request. Use safeParse() and return 400 Bad Request with error messages. Reserve parse() for internal trusted data.

🔀Coerce for URL params and query strings

URL params and query strings are always strings in Express/Next.js. z.coerce.number() converts '42' → 42 before validation. Without coerce, z.number().parse('42') fails.

Discussion