UnblockDevs
All tools

Mock API Generator – Create Fake REST APIs Instantly

Dynamic responses, auth simulation, latency, rate limiting, conditional rules. Export to Postman & OpenAPI.

100% in-browserNo signupFree forever

Mock API Generator

Create REST endpoints with dynamic responses, auth simulation, latency, and error scenarios. Export to Postman or OpenAPI.

Quick start:

Endpoint

0–10000 ms to simulate real API delay

Response

+ uuid, name, email, timestamp, random_int, random_bool, ip, country, id

Learn more

Free Mock API in Seconds

Generate fake endpoints with delay, status codes, and pagination for frontend development.

Read guide →

What Is a Mock API?

A mock API is a simulated REST API that returns predefined responses without connecting to a real backend. Instead of wiring up a database and server, you define routes, status codes, and JSON bodies — and the mock behaves exactly like a real API from the perspective of any client calling it.

Mock APIs are a standard practice in modern frontend development. They let you build and test UI components before the backend exists, reproduce error scenarios that are hard to trigger in production, and run automated tests without network dependencies. When the real API is ready, you simply swap the base URL and nothing in your frontend code changes.

How it works

Generate Mock Data in Seconds

01

Define your endpoint

Set the HTTP method (GET, POST, PUT, DELETE, PATCH), the route path, and an optional response delay to simulate latency.

02

Configure the response

Choose a status code, write or auto-generate the JSON body using realistic field types: names, emails, UUIDs, dates, and more.

03

Add optional rules

Simulate auth (API key or Bearer token), configure rate limits, or set up conditional responses based on request parameters.

04

Export and integrate

Copy the mock config, export a Postman collection or OpenAPI spec, and point your frontend at the mock to start developing immediately.

Use cases

When Developers Use Mock APIs

🖥️

Frontend Without Backend

Build complete UI features and data flows before the backend API exists — no blockers, no waiting on other teams.

🧪

Unit & Integration Tests

Write deterministic tests against a mock that always returns the same response, no matter the network state.

🎨

Demo & Prototype Data

Populate a product demo or clickable prototype with realistic-looking data without exposing real user information.

📄

API Documentation

Pair your API docs with a live mock so readers can make real requests against working endpoints immediately.

📈

Load & Performance Testing

Run load tests against a mock that responds instantly to benchmark your client code without hitting production rate limits.

✈️

Offline Development

Keep working on planes, trains, and coffee shops where the real API is unreachable by switching to a local mock.

Supported Mock Data Types

The generator supports realistic field types so your mock responses look like real production data:

TypeExample OutputCommon Use
NameJane DoeUser profiles, author fields
Emailjane@example.comAccount data, contact lists
UUIDa1b2c3d4-…Resource IDs, entity keys
Date2024-06-15T10:30:00ZCreated/updated timestamps
Phone+1-555-123-4567Contact forms, user records
Address123 Main St, SpringfieldShipping, billing, location data
Number42 / 3.14Counts, prices, scores
Booleantrue / falseFeature flags, status fields
FAQ

Frequently Asked Questions

1What is a mock API?
A mock API is a fake REST API that returns predefined responses without a real backend. It is used during frontend development and testing to simulate API behavior when the real service is not available or too costly to call.
2What is the difference between a mock, a stub, and a fake?
A stub returns hardcoded responses with no logic. A mock verifies that specific calls were made — commonly used in unit tests. A fake is a working substitute for a real service. In practice, "mock API" is used loosely to mean any server that returns realistic fake responses for development.
3Can I simulate errors and edge cases?
Yes. You can configure any HTTP status code (400, 401, 404, 500, etc.) as the response, add a delay to simulate timeout conditions, and set up conditional rules to return different responses based on query parameters or request body fields.
4When should I use a mock API instead of the real one?
Use a mock when the real API is not ready, has rate limits or per-call costs, when you need deterministic test data, when you want to develop offline, or when you need to reliably reproduce edge cases and error states.
5Is my mock data sent to a server?
No. All mock generation happens entirely in your browser. Your endpoint definitions, JSON bodies, and any sensitive field values never leave your device.
6How do I create a mock REST API without a backend?
Define your endpoints, HTTP methods, status codes, and JSON response bodies in the Mock API Generator, then export a Postman collection or OpenAPI spec. For local development, tools like json-server, WireMock, or MSW let you serve these locally.
7What is the difference between Mock Service Worker and a mock API generator?
MSW intercepts network requests at the service worker level in the browser or Node.js — ideal for unit tests. A mock API generator creates a standalone server config or spec file that any HTTP client can call, useful for prototyping and cross-team collaboration.
8Can I simulate authentication in a mock API?
Yes. The tool supports auth simulation including API key and Bearer token validation. Configure the mock to return 401 Unauthorized for missing tokens and 200 OK for valid ones so your frontend auth flows work end-to-end.
9How do I export a mock API to Postman?
After configuring your mock endpoints, click Export Postman Collection to download a Postman v2.1-compatible JSON file. Import it into Postman to get a pre-built collection with all endpoints, example bodies, and expected responses ready to run.
10How do I simulate API errors and edge cases?
Configure the HTTP status code to 400, 401, 404, 429, or 500 for any endpoint. Add response delay to simulate timeouts. This makes it easy to test error handling and loading states without touching a real API.
11How do I generate a mock API from an OpenAPI spec?
Export your mock configuration as an OpenAPI (Swagger) spec using the Export OpenAPI button. You can then use tools like Prism or Stoplight Studio to serve the spec as a live mock server, or import it into Postman for automated API testing.
12What is the difference between a mock API and a stub API?
A stub returns hardcoded responses with no logic. A mock can include conditional logic, verify specific requests, simulate auth, and return different responses based on request parameters — making it more flexible for realistic testing.
Learn more

Developer Guides

📖Mock API Design Guide📖JSON API Best Practices📖API Testing Strategies📖Debugging Mock Responses

Feedback for mock_api_generator

Tell us what's working, what's broken, or what you wish we built next — it directly shapes our roadmap.

You make the difference

Good feedback is gold — a rough edge you hit today could be smoother for everyone tomorrow.

  • Feature ideas often jump the queue when lots of you ask.
  • Bug reports with steps get fixed faster — paste URLs or examples if you can.
  • Name and email are optional; we won't use them for anything except replying if needed.

Stay Updated

Get the latest tool updates, new features, and developer tips delivered to your inbox.

What you'll get
  • Product updates & new tools
  • JSON, API & developer tips
  • Unsubscribe anytime — no hassle

Get in touch

Feature ideas, bugs, or a quick thanks — we read every message.

support@unblockdevs.com