What is Zod?
Zod is a TypeScript-first schema declaration and runtime validation library. A Zod schema describes the shape and constraints of a value — strings, numbers, objects, arrays, unions — and can parse, validate, and transform input at runtime, inferring the TypeScript type automatically so that compile-time types and runtime validation are always in sync.
Traditional TypeScript type annotations disappear at compile time — the runtime receives untyped data from APIs, user input, and environment variables with no safety guarantees. Zod bridges this gap by generating both a TypeScript type and a runtime validator from a single schema definition.
Defining a schema like z.object({ name: z.string(), age: z.number().min(0) }) gives you a TypeScript type (automatically inferred with z.infer<typeof schema>), a parse function that throws a detailed ZodError if input does not conform, and a safeParse function that returns { success: true, data } or { success: false, error } without throwing.
Zod schemas compose: z.union(), z.intersection(), z.discriminatedUnion(), z.record(), z.tuple(), z.enum(), and z.literal() cover most data shapes. Transformations (z.string().transform(s => s.trim())) and refinements (z.number().refine(n => n % 2 === 0, "must be even")) extend validation beyond simple type-checking. .optional(), .nullable(), and .default() handle missing values.
Zod has become the de facto standard for TypeScript form validation (react-hook-form, @tanstack/form), API input validation (Next.js route handlers, tRPC), environment variable parsing (the t3-env package), and configuration validation. Its tight TypeScript integration means editors autocomplete validated field names and types throughout the codebase.
quickhelp.dev uses Zod for every tool's inputSchema and outputSchema. These schemas serve four purposes simultaneously: runtime API input validation, OpenAPI 3.1 JSON Schema generation, MCP tool descriptor generation, and automatic UI form generation — one schema, four surfaces, zero duplication.