Zod
TypeScript-first schema validation with static type inference
by @colinhacks
Docs β’ Discord β’ π β’ Bluesky
What is Zod?
Zod is a TypeScript-first validation library. Define a schema and parse some data with it. You'll get back a strongly typed, validated result.
import * as z from "zod";
const User = z.object({
name: z.string(),
});
// some untrusted data...
const input = {
/* stuff */
};
// the parsed result is validated and type safe!
const data = User.parse(input);
// so you can use it with confidence :)
console.log(data.name);Features
- Zero external dependencies
- Works in Node.js and all modern browsers
- Tiny:
2kb core bundle (gzipped) - Immutable API: methods return a new instance
- Concise interface
- Works with TypeScript and plain JS
- Built-in JSON Schema conversion
- Extensive ecosystem
Installation
npm install zod
Basic usage
Before you can do anything else, you need to define a schema. For the purposes of this guide, we'll use a simple object schema.
import * as z from "zod";
const Player = z.object({
username: z.string(),
xp: z.number(),
});Parsing data
Given any Zod schema, use .parse to validate an input. If it's valid, Zod returns a strongly-typed deep clone of the input.
Player.parse({ username: "billie", xp: 100 });
// => returns { username: "billie", xp: 100 }Note β If your schema uses certain asynchronous APIs like async refinements or transforms, you'll need to use the .parseAsync() method instead.
const schema = z.string().refine(async (val) => val.length "hello"
AOT compilation
For hot validation paths, z.compile(schema) returns a schema clone with an ahead-of-time compiled fast path. Valid inputs take the compiled path; invalid inputs fall back to the regular parser so error reporting stays identical.
Across a 55-schema benchmark the median speedup is 2.4x, and it scales with how much work the schema does per parse: a large array of objects is ~9x, a 20-key object ~9x, a nested object ~4.5x, while a bare z.string() gains nothing β compilation removes per-node dispatch and allocation, and a single typeof has none to remove.
const CompiledPlayer = z.compile(Player);
CompiledPlayer.parse({ username: "billie", xp: 100 });To enable compilation globally for schemas constructed after import:
import "zod/compile"; // place before modules that define schemas
Things to know:
- Compilation uses
new Function. Global mode is automatically disabled when z.config({ jitless: true }) is set (e.g. CSP environments); calling z.compile() directly is an explicit opt-in. - Schemas with async refinements or transforms can't be compiled, and neither can a few other constructs. That is not an error:
z.compile() hands the schema back unchanged and it keeps using the regular parser, exactly as global mode leaves it. Pass { strict: true } to throw ZodCompileAsyncError / ZodCompileUnsupportedError instead. - On invalid input, refinements and transforms may run twice (fast path, then fallback).
- Deriving a new schema from a compiled one (
.refine(), .extend(), etc.) returns an uncompiled schema β compile the final schema.
See `compile` docs for details.
Handling errors
When validation fails, the .parse() method will throw a ZodError instance with granular information about the validation issues.
try {
Player.parse({ username: 42, xp: "100" });
} catch (err) {
if (err instanceof z.ZodError) {
err.issues;
/* [
{
expected: 'string',
code: 'invalid_type',
path: [ 'username' ],
message: 'Invalid input: expected string, received number'
},
{
expected: 'number',
code: 'invalid_type',
path: [ 'xp' ],
message: 'Invalid input: expected number, received string'
}
] */
}
}To avoid a try/catch block, you can use the .safeParse() method to get back a plain result object containing either the successfully parsed data or a ZodError. The result type is a discriminated union, so you can handle both cases conveniently.
const result = Player.safeParse({ username: 42, xp: "100" });
if (!result.success) {
result.error; // ZodError instance
} else {
result.data; // { username: string; xp: number }
}Note β If your schema uses certain asynchronous APIs like async refinements or transforms, you'll need to use the .safeParseAsync() method instead.
const schema = z.string().refine(async (val) => val.length { success: true; data: "hello" }Inferring types
Zod infers a static type from your schema definitions. You can extract this type with the z.infer utility and use it however you like.
const Player = z.object({
username: z.string(),
xp: z.number(),
});
// extract the inferred type
type Player = z.infer;
// use it in your code
const player: Player = { username: "billie", xp: 100 };In some cases, the input & output types of a schema can diverge. For instance, the .transform() API can convert the input from one type to another. In these cases, you can extract the input and output types independently:
const mySchema = z.string().transform((val) => val.length);
type MySchemaIn = z.input;
// => string
type MySchemaOut = z.output; // equivalent to z.infer
// number