Transforms

Zod · Reference cheat sheet

📋 Overview

Transforms change values during parsing: trim strings, normalize casing, map DTOs, or convert types. Output types can differ from input types.

API	Role
`.transform(fn)`	Map value after validation
`.pipe(schema)`	Feed output into another schema
`z.preprocess`	Run before validation
Input vs output	`z.input<typeof S>` / `z.output<typeof S>`

Trim email:

const Email = z
  .string()
  .trim()
  .toLowerCase()
  .email();

Transform shape:

const Raw = z.object({ user_id: z.string() }).transform((d) => ({
  userId: d.user_id,
}));

Pipe:

const IsoDate = z.string().datetime().pipe(z.coerce.date());

Transforms run on success path — failed refinements skip later transforms.
Inferred z.infer is the output type; use z.input when typing forms that submit raw values.
Overusing preprocess can hide invalid data instead of failing loudly.