Writing Zod Transformations

Purpose

Comprehensive guide to writing transformations in Zod v4, covering built-in string methods, custom transforms, codecs, and transformation pipelines.

Built-In String Transformations

Trim, Lower Case, Upper Case

const schema = z.string().trim();           // Remove whitespace
const schema = z.string().toLowerCase();    // Convert to lowercase
const schema = z.string().toUpperCase();    // Convert to uppercase

Use cases:

• Trim: User input fields (always trim)
• Lower: Email/username normalization