About ApiSimul / the switchboard
01 Why we built this
Every front-end developer has lived the same week: the UI is ready, the endpoints are not, and a spreadsheet of "sample responses" stands in for an API. ApiSimul replaces that waiting with a switchboard you operate yourself.
The problem
Front-end work stalls when back-end endpoints are late. Developers paste hardcoded arrays into components, then spend days unwiring them. Contract changes ripple through fixtures nobody remembers updating, and slow-or-error states simply never get tested until production.
The solution
A Service Worker that sits between your page and the network. You write routing rules the way the real API is meant to behave — method, path params, status, headers, latency, and a response template full of dynamic fake data. Your app's real fetch() calls get answered on the spot.
How it works
Everything runs client-side: the rule board lives in your browser's IndexedDB, the matching engine and placeholder renderer are plain JavaScript, and the interception is the browser's own Service Worker API. There is no mock server to install and no tunnel to keep alive.
Who it's for
Front-end developers building against unfinished APIs, teams prototyping interfaces before a contract is signed, QA engineers reproducing error paths, and instructors teaching how apps behave under slow or failing networks.
02 What we believe
Three commitments shaped the switchboard.
No invasion
Mocking should not require touching your application code. Interception happens at the browser level, so the same components that will call the real API one day call the mock today. Uninstall the operator and nothing is left behind.
Honest responses
A mock that returns the same object every time tests nothing. Placeholders regenerate on every call, repeat blocks build whole arrays, latency and status are first-class settings — so loading spinners, empty states, and error handlers all get exercised for real.
Local by default
Your rules and logs never leave the browser. Export them as JSON when you want to share, import them on a teammate's machine, and otherwise treat the board as your own private piece of infrastructure.