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TypeScript Academy · Lesson

Runtime validation with zod (intro)

Validate JSON responses at runtime with zod schemas to ensure safety beyond compile-time types.

Runtime validation with zod (intro) is a free TypeScript Academy lesson on CoddyKit — lesson 2 of 2. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the TypeScript Academy learning path, one of 2 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Intro

Goal: Add runtime safety with zod. Compile-time types are not enough, so schemas validate live data.

Install zod

Install zod, a popular runtime schema validation library for TS/JS.

npm install zod

Schema definition

Create schemas with z.object(). Use z.infer<typeof Schema> to generate TS types from schemas.

import { z } from "zod";

const UserSchema = z.object({
  id: z.number(),
  name: z.string()
});

type User = z.infer<typeof UserSchema>;

Schema.parse()

Call Schema.parse() to validate data. Throws an error if JSON does not match the schema.

async function getUser() {
  const res = await fetch("/user.json");
  const raw = await res.json();
  const parsed = UserSchema.parse(raw);
  console.log(parsed.id, parsed.name);
}

safeParse

safeParse returns an object with success and error fields. Safer than throwing exceptions.

const result = UserSchema.safeParse(raw);
if (!result.success) {
  console.error(result.error);
} else {
  console.log(result.data);
}

Nested schema

Schemas can be nested: arrays, objects, optional fields, etc.

const PostSchema = z.object({
  id: z.number(),
  title: z.string(),
  tags: z.array(z.string())
});

const raw = { id: 1, title: "Hello", tags: ["ts", "zod"] };
const post = PostSchema.parse(raw);

Validation check

Quick check: Why use zod validation after parsing JSON?

Recap

Recap: zod schemas validate runtime JSON. Use parse or safeParse to ensure safety.

Frequently asked questions

Is the “Runtime validation with zod (intro)” lesson free?

Yes — the full text of “Runtime validation with zod (intro)” is free to read here on the web, and the TypeScript Academy course includes 2 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the TypeScript Academy course, upgrade to CoddyKit PRO.

What will I learn in “Runtime validation with zod (intro)”?

Validate JSON responses at runtime with zod schemas to ensure safety beyond compile-time types. You practise TypeScript Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start TypeScript Academy?

No prior experience is required. TypeScript Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 2, so you can start here or from the beginning and move at your own pace.

How long does the “Runtime validation with zod (intro)” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this TypeScript Academy lesson?

Yes. Every TypeScript Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Fetch API types; Response.json() generics
  2. Runtime validation with zod (intro)
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