json-schema-to-zod

What is json-schema-to-zod?

The json-schema-to-zod package is a tool that converts JSON Schema definitions into Zod schemas. Zod is a TypeScript-first schema declaration and validation library, and this package helps in bridging the gap between JSON Schema and Zod by automating the conversion process.

What are json-schema-to-zod's main functionalities?

Convert JSON Schema to Zod Schema

This feature allows users to convert a JSON Schema into a Zod schema. The code sample demonstrates how to use the `jsonSchemaToZod` function to transform a JSON Schema object into a Zod schema, which can then be used for validation in a TypeScript environment.

const { jsonSchemaToZod } = require('json-schema-to-zod');

const jsonSchema = {
  type: 'object',
  properties: {
    name: { type: 'string' },
    age: { type: 'number' }
  },
  required: ['name', 'age']
};

const zodSchema = jsonSchemaToZod(jsonSchema);
console.log(zodSchema.toString());

Other packages similar to json-schema-to-zod

ajv

AJV is a JSON Schema validator that is highly performant and supports JSON Schema draft-07 and later. Unlike json-schema-to-zod, AJV focuses on validating data against JSON Schemas directly rather than converting them to another format like Zod.

joi

Joi is a powerful schema description language and data validator for JavaScript. While it does not directly convert JSON Schema to its format, it serves a similar purpose in defining and validating data schemas, similar to what Zod does after conversion.

typescript-json-schema

This package generates JSON Schema from TypeScript types. It serves the opposite purpose of json-schema-to-zod by converting TypeScript definitions into JSON Schema, rather than converting JSON Schema into another validation format.

README

Json-Schema-to-Zod

Looking for the exact opposite? Check out zod-to-json-schema

Summary

A runtime package and CLI tool to convert JSON schema (draft 4+) objects or files into Zod schemas in the form of JavaScript code.

Before v2 it used prettier for formatting and json-refs to resolve schemas. To replicate the previous behaviour, please use their respective CLI tools.

Since v2 the CLI supports piped JSON.

Usage

Online

Just paste your JSON schemas here!

CLI

Simplest example

npm i -g json-schema-to-zod

json-schema-to-zod -i mySchema.json -o mySchema.ts

Example with $refs resolved and output formatted

npm i -g json-schema-to-zod json-refs prettier

json-refs resolve mySchema.json | json-schema-to-zod | prettier --parser typescript > mySchema.ts

Options

Flag	Shorthand	Function
--input	-i	JSON or a source file path. Required if no data is piped.
--output	-o	A file path to write to. If not supplied stdout will be used.
--name	-n	The name of the schema in the output
--depth	-d	Maximum depth of recursion in schema before falling back to z.any(). Defaults to 0.
--module	-m	Module syntax; esm, cjs or none. Defaults to esm in the CLI and none programmaticly.
--type	-t	Export a named type along with the schema. Requires name to be set and module to be esm.
--noImport	-ni	Removes the import { z } from 'zod'; or equivalent from the output.
--withJsdocs	-wj	Generate jsdocs off of the description property.

Programmatic

Simple example

import { jsonSchemaToZod } from "json-schema-to-zod";

const myObject = {
  type: "object",
  properties: {
    hello: {
      type: "string",
    },
  },
};

const module = jsonSchemaToZod(myObject, { module: "esm" });

// `type` can be either a string or - outside of the CLI - a boolean. If its `true`, the name of the type will be the name of the schema with a capitalized first letter.
const moduleWithType = jsonSchemaToZod(myObject, {
  name: "mySchema",
  module: "esm",
  type: true,
});

const cjs = jsonSchemaToZod(myObject, { module: "cjs", name: "mySchema" });

const justTheSchema = jsonSchemaToZod(myObject);

module

import { z } from "zod";

export default z.object({ hello: z.string().optional() });

moduleWithType

import { z } from "zod";

export const mySchema = z.object({ hello: z.string().optional() });
export type MySchema = z.infer<typeof mySchema>;

cjs

const { z } = require("zod");

module.exports = { mySchema: z.object({ hello: z.string().optional() }) };

justTheSchema

z.object({ hello: z.string().optional() });

Example with $refs resolved and output formatted

import { z } from "zod";
import { resolveRefs } from "json-refs";
import { format } from "prettier";
import jsonSchemaToZod from "json-schema-to-zod";

async function example(jsonSchema: Record<string, unknown>): Promise<string> {
  const { resolved } = await resolveRefs(jsonSchema);
  const code = jsonSchemaToZod(resolved);
  const formatted = await format(code, { parser: "typescript" });

  return formatted;
}

Overriding a parser

You can pass a function to the overrideParser option, which represents a function that receives the current schema node and the reference object, and should return a string when it wants to replace a default output. If the default output should be used for the node just return void.

Schema factoring

Factored schemas (like object schemas with "oneOf" etc.) is only partially supported. Here be dragons.

Use at Runtime

The output of this package is not meant to be used at runtime. JSON Schema and Zod does not overlap 100% and the scope of the parsers are purposefully limited in order to help the author avoid a permanent state of chaotic insanity. As this may cause some details of the original schema to be lost in translation, it is instead recommended to use tools such as Ajv to validate your runtime values directly against the original JSON Schema.

That said, it's possible in most cases to use eval. Here's an example that you shouldn't use:

const zodSchema = eval(jsonSchemaToZod({ type: "string" }, { module: "cjs" }));

zodSchema.safeParse("Please just use Ajv instead");