About ApiSimul / the switchboard
APISimul is a small, independent project. A browser-based API mock simulator is the whole of what we do here: it intercepts fetch and XHR calls with a service worker so you can test a front end against fake endpoints without running a backend. There is no account to create, no email to hand over, and no paywall hiding behind the third advert.
Why this site exists
Plenty of developer pages already exist. Most of them make you dismiss a banner, ignore a modal and scroll past filler before the tool appears. APISimul inverts that: the tool is the page, it intercepts fetch and XHR calls with a service worker so you can test a front end against fake endpoints without running a backend, and everything else is explanation you can read or skip.
How it works
No server is involved in the arithmetic. The service worker registers a request handler that matches your rules by method and URL pattern, then returns the status code, latency and JSON body you configured before the request ever reaches the network. We state the method openly because a tool that cannot explain its own answer is not much use to anyone trying to trust it.
What happens to your input
Nothing you enter is transmitted. The mock rules, status codes and response bodies you define are handled by the page on your own machine, which is why APISimul has no server-side copy to lose, leak or hand over — and why it still works once you go offline.
Who this is for
- programmers tidying up a payload or a schema.
- engineers debugging something at short notice.
- anyone who would rather not paste a token into a server.
Keeping it free
Advertising pays for the running of APISimul; nothing here is subscription-based. No advertiser is given the values you enter, and an advert appearing beside a tool is never a recommendation of it.
Get in touch
Tell us through the contact page if you find a bug or want something added. The browser-based API mock simulator improves mainly on the strength of what users report.