A Mockoon alternative with nothing to design

Mockoon is an open-source desktop application, with a CLI and Docker image for running the same mocks headless, for creating mock APIs locally. You define routes, responses, headers and status codes in a GUI; rules pick a response based on the request, templating produces dynamic bodies, and it can import an OpenAPI document to start from.

At a glance

Mockoon compared with this playground, checked 2026-09.
	Mockoon	Fun API Playground
What it is	A desktop app and CLI for building mocks	A ready-made simulated API catalog
Who defines responses	You	The playground
Custom contract	Yes	No
Realistic failures without setup	No	Yes
Runs offline	Yes	Yes, in the browser
OpenAPI	Import to create mocks	Exported for every API
Best for	Standing in for an API you are building against	Practising against an API you do not control

Where it stops

Like every configurable mock, it does exactly what you designed. That is ideal for standing in for an API whose contract you know and for working offline, and it means the behaviour is never more realistic than the time you put into it. Persistent, constrained state — stock that runs out, versions that move, a seat someone else took — is possible to approximate and laborious to build.

What is different here

Here there is no design step. Thirty-nine APIs already exist with state that persists per caller and constraints that produce failures for a reason, so a test meets the kind of behaviour a real third-party API has. The trade-off is control: you cannot change the contract, only learn it.

What Mockoon does better

Your own endpoints and responses, shaped to the contract you need.
A GUI that makes creating and editing mocks approachable.
Runs locally and offline, and headless in CI through the CLI or Docker.
Can start from an existing OpenAPI document.

What this playground does better

Nothing to design, install or keep running.
Behaviour is realistic out of the box: conflicts, preconditions, rate limits, async jobs, token expiry.
Per-caller persistent state over a public HTTPS API as well as in the browser.
Practice material — guides, challenges and a glossary — built around the same APIs.

Which to use

Choose Mockoon to stand in for a specific API you know, locally and offline. Choose this to practise and learn against APIs whose rules you did not write.

Checked against Mockoon as of 2026-09.

Other comparisons

JSONPlaceholder — JSONPlaceholder fakes its writes. If you need a POST that a later GET can find, that is the difference.
httpbin — httpbin shows you the request. This shows you an API. They answer different questions.
reqres.in — reqres is a clean, tiny user API with fake auth. The gap is everything past the happy path.
json-server — json-server turns a JSON file into a REST API in seconds. It does not push back — and that is the difference.
WireMock — WireMock reproduces the API you already know, exactly. This one gives you an API you do not control.
Beeceptor — Beeceptor gives you a hosted endpoint to inspect and mock. This gives you finished APIs that behave like real ones.
DummyJSON — DummyJSON has rich sample data and a JWT login. Its writes are simulated; here they persist.
Postman mock servers — A Postman mock server replays the examples saved in a collection. This one runs an API with state and rules.
PokeAPI — PokeAPI is the real Pokémon database, read-only. This Pokémon API is invented data you can write to and break.
SWAPI — SWAPI serves Star Wars data, read-only. This Star Wars API is invented practice data you can change.
the free mock API landscape — Six free options, what each is genuinely for, and how to tell which one your problem needs.

All 39 mock REST APIs · Getting started guide · About this playground

Last updated 15 October 2026