For library authors

This page is primarily intended for consumption by library authors who are building tooling on top of Zod.

Do I need to depend on Zod?

First things first, make sure you need to depend on Zod at all.

If you're building a library that accepts user-defined schemas to perform black-box validation, you may not need to integrate with Zod specifically. Instead look into Standard Schema. It's a shared interface implemented by most popular validation libraries in the TypeScript ecosystem (see the full list), including Zod.

This spec works great if you accept user-defined schemas and treat them like "black box" validators. Given any compliant library, you can extract inferred input/output types, validate inputs, and get back a standardized error.

If you need Zod specific functionality, read on.

How to configure peer dependencies?

Any library built on top of Zod should include "zod" in "peerDependencies". This lets your users "bring their own Zod".

// package.json
{
  // ...
  "peerDependencies": {
    "zod": "^3.25.0"
  }
}

During development, you need to meet your own peer dependency requirement, to do so, add "zod" to your "devDependencies" as well.

// package.json
{
  "peerDependencies": {
    "zod": "^3.25.0"
  },
  "devDependencies": {
    "zod": "^3.25.0"
  }
}

How to support Zod 4?

To support Zod 4, update the minimum version for your "zod" peer dependency to ^3.25.0.

// package.json
{
  // ...
  "peerDependencies": {
    "zod": "^3.25.0"
  }
}

Starting with v3.25.0, the Zod 4 core package is available at a /v4/core subpath. Read the Versioning in Zod 4 writeup for full context on this versioning approach.

import * as z4 from "zod/v4/core";

Import from these subpaths only. Think of them like "permalinks" to their respective Zod versions. These will remain available forever.

• "zod/v3" for Zod 3 ✅
• "zod/v4/core" for the Zod 4 Core package ✅

Do not import from these subpaths:

• "zod" — ❌ In 3.x releases, this exports Zod 3. In a future 4.x release, this will export Zod 4. Use the permalinks instead.
• "zod/v4"— ❌ This subpath is the home of Zod 4 "Classic". If you reference classes from the standard module, your library will not work with Zod Mini. This is extremely discouraged. Use "zod/v4/core" instead, which exports the $-prefixed subclasses that are extended by Zod Classic and Zod Mini. The internals of the classic & mini subclasses are identical; they only differ in which helper methods they implement.

Do I need to publish a new major version?

No, you should not need to publish a new major version of your library to support Zod 4 (unless you are dropping support for Zod 3, which isn't recommended).

You will need to bump your peer dependency to ^3.25.0, thus your users will need to npm upgrade zod. But there were no breaking changes made to Zod 3 between zod@3.24 and zod@3.25; in fact, there were no code changes whatsoever. As code changes will be required on the part of your users, I do not believe this constitutes a breaking change. I recommend against publishing a new major version.

How to support Zod 3 and Zod 4 simultaneously?

Starting in v3.25.0, the package contains copies of both Zod 3 and Zod 4 at their respective subpaths. This makes it easy to support both versions simultaneously.

import * as z3 from "zod/v3";
import * as z4 from "zod/v4/core";
 
type Schema = z3.ZodTypeAny | z4.$ZodType;
 
function acceptUserSchema(schema: z3.ZodTypeAny | z4.$ZodType) {
  // ...
}

To differentiate between Zod 3 and Zod 4 schemas at runtime, check for the "_zod" property. This property is only defined on Zod 4 schemas.

import type * as z3 from "zod/v3";
import type * as z4 from "zod/v4/core";
 
declare const schema: z3.ZodTypeAny | v4.$ZodType;
 
if ("_zod" in schema) {
  schema._zod.def; // Zod 4 schema
} else {
  schema._def; // Zod 3 schema
}

How to support Zod and Zod Mini simultaneously?

Your library code should only import from "zod/v4/core". This sub-package defines the interfaces, classes, and utilities that are shared between zod/v4 and zod/v4-mini.

// library code
import * as z4 from "zod/v4/core";
 
export function acceptObjectSchema<T extends z4.$ZodObject>(schema: T){
  // parse data
  z4.parse(schema, { /* somedata */});
  // inspect internals
  schema._zod.def.shape;
}

By building against the shared base interfaces, you can reliably support both sub-packages simultaneously. This function can accept both zod/v4 and zod/v4-mini schemas.

// user code
import { acceptObjectSchema } from "your-library";
 
// Zod 4
import * as z from "zod/v4";
acceptObjectSchema(z.object({ name: z.string() }));
 
// Zod 4 Mini
import * as zm from "zod/v4-mini";
acceptObjectSchema(zm.object({ name: zm.string() }))

Refer to the Zod Core page for more information on the contents of the core sub-library.

How to accept user-defined schemas?

Accepting user-defined schemas is the a fundamental operation for any library built on Zod. This section outlines the best practices for doing so.

When starting out, it may be tempting to write a function that accepts a Zod schema like this:

import * as z4 from "zod/v4/core";
 
function inferSchema<T>(schema: z4.$ZodType<T>) {
  return schema;
}

This approach is incorrect, and limits TypeScript's ability to properly infer the argument. No matter what you pass in, the type of schema will be an instance of $ZodType.

inferSchema(z.string());
// => $ZodType<string>

This approach loses type information, namely which subclass the input actually is (in this case, ZodString). That means you can't call any string-specific methods like .min() on the result of inferSchema. Instead, your generic parameter should extend the core Zod schema interface:

function inferSchema<T extends z4.$ZodType>(schema: T) {
  return schema;
}
 
inferSchema(z.string());
// => ZodString ✅

To constrain the input schema to a specific subclass:

 
import * as z4 from "zod/v4/core";
 
// only accepts object schemas
function inferSchema<T>(schema: z4.$ZodObject) {
  return schema;
}

To constrain the inferred output type of the input schema:

 
import * as z4 from "zod/v4/core";
 
// only accepts string schemas
function inferSchema<T extends z4.$ZodType<string>>(schema: T) {
  return schema;
}
 
inferSchema(z.string()); // ✅ 
 
inferSchema(z.number()); 
// ❌ The types of '_zod.output' are incompatible between these types. 
// // Type 'number' is not assignable to type 'string'

To parse data with the schema, use the top-level z4.parse/z4.safeParse/z4.parseAsync/z4.safeParseAsync functions. The z4.$ZodType subclass has no methods on it. The usual parsing methods are implemented by Zod and Zod Mini, but are not available in Zod Core.

function parseData<T extends z4.$ZodType>(data: unknown, schema: T): z4.output<T> {
  return z.parse(schema, data);
}
 
parseData("sup", z.string());
// => string