API Mock & Schema Studio
Build your interface without waiting for backend services. Paste your OpenAPI 3.1 and JSON Schema contracts to instantly generate realistic Mock JSON data, TypeScript interfaces, Zod schemas and Next.js Route Handler code.
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Paste OpenAPI or JSON Schema, or pick the ready-made e-commerce/user preset.
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Switch to the Mock JSON, TypeScript models, Zod validator or Next.js API handler tab.
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A Guide to Mock Data and Type Safety with OpenAPI 3.1 & JSON Schema
In modern software engineering, frontend and backend teams waiting on each other (a blocking dependency) is one of the bottlenecks that slows delivery cycles the most. Contract-First Development solves this by making the API schema the Single Source of Truth. API Mock & Schema Studio processes your OpenAPI 3.1 and JSON Schema definitions directly in your browser and generates rich mock JSON data, TypeScript models, Zod schemas and Next.js Route Handler code in seconds.
1. Contract-First Development and Zero-Blocking
In traditional workflows, everyone waits for backend developers to finish the database models and endpoints. This delays frontend, mobile and test teams by weeks. With the Contract-First approach, teams first agree on an OpenAPI (Swagger) or JSON Schema definition. As soon as the contract is final, this tool lets:
- Frontend Developers: Build UI components, pagination and state management in full with realistic mock data.
- Mobile Teams: Test iOS (Swift) and Android (Kotlin) clients early with type-safe mock data.
- QA and Test Engineers: Verify edge cases, enum values and error scenarios without needing a live service.
2. How Does Smart Mock Data Generation Work?
The studio walks the schema tree recursively and assigns the most suitable values based on field metadata:
Generates a standard RFC 4122 v4 UUID (e.g. 550e8400-e29b-41d4...).
Generates valid ISO 8601 timestamps that work directly with date libraries.
Automatically picks the first valid option from the defined enum set.
Provides realistic prototype data for names such as email, name, avatar, currency and price.
3. Using TypeScript and Runtime Zod Validation Together
TypeScript interfaces stop you from making mistakes at compile time, but they cannot check at runtime whether the data reaching the client matches the contract. That is why modern Next.js 15+ and React 19 projects use both interface and z.object schemas together. With the generated Zod schema, you can validate API responses like this:
import { OrderSchema } from '@/lib/schemas'
export async function fetchOrder(id: string) {
const res = await fetch(`/api/orders/${id}`)
const json = await res.json()
// Runtime validation: missing or wrong types that break the schema are caught immediately
const validated = OrderSchema.safeParse(json)
if (!validated.success) {
console.error('API contract violation:', validated.error.flatten())
throw new Error('Invalid API response')
}
return validated.data // A fully type-safe Order object
}4. Mock API Architecture with the Next.js 15+ App Router
You can drop the code from the studio's Next.js Route Handler tab straight into your project's app/api/[resource]/route.ts file. With an environment variable (for example NEXT_PUBLIC_USE_MOCK_API=true) you call this mock route in development and the real backend service in production, moving to production without changing a single line of code.
5. Security, Privacy and a 100% Client-Side Guarantee
In enterprise projects and proprietary product development, API schemas, data models and internal terminology are confidential. API Mock & Schema Studio runs all schema parsing, data generation and type creation only in your browser's JavaScript engine. Your data is never stored on any server, logged or shared with third-party services.
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