Custom schemas

You can create a Zod schema for any TypeScript type by using z.custom(). This is useful for creating schemas for types that are not supported by Zod out of the box, such as template string literals.

const px = z.custom<`${number}px`>(val => {
  return typeof val === "string" ? /^\d+px$/.test(val) : false;
});
 
type px = z.infer<typeof px>; // `${number}px`
 
px.parse("42px"); // "42px"
px.parse("42vw"); // throws;

If you don't provide a validation function, Zod will allow any value. This can be dangerous!

z.custom<{ arg: string }>(); // performs no validation

You can customize the error message and other options by passing a second argument. This parameter works the same way as the params parameter of .refine.

z.custom<...>((val) => ..., "custom error message");