Create a simulation

Updated Aug 30, 2026·2 min read

A new simulation is a container with a URL of its own and nothing in it yet. Creating one serves nothing; endpoints appear at the URL only after a deploy.

Ways to start

Open Simulations and click New simulation to start blank, or pick another start from the arrow next to it:

Blank simulation starts from scratch; you add endpoints and specs yourself.
Sample simulation comes prefilled with the Petstore spec and a few static endpoints. The Quickstart walks through it.
Browse catalog starts from a curated API: Stripe, Twilio, Auth0 and more. See Start from the catalog.
Backend sandbox is a different kind of simulation: a payment or identity provider run as your own sandbox. See Create a sandbox.

Your own OpenAPI spec is added inside the simulation once it exists, whichever way you started.

See Upload and update an OpenAPI spec.

A simulation can also be deployed straight from a GitHub repo, with a URL per branch and pull request.

See GitHub Action.

Name, domain and slug

Starting blank opens this dialog:

Name is the display name shown in lists. Change it any time.
Domain picks which API host the simulation's URL uses. The default is fine.
Slug becomes part of the URL: <domain>/app/<your-org>/<slug>. Lowercase letters, digits and hyphens, kept short; the form checks availability as you type.

A deployed simulation cannot change its slug. Take it offline first, rename it, then deploy again.

A simulation counts against your plan's allowance from the moment it is created, deployed or not. Deleting one frees the slot.

After creating

The simulation opens on its Endpoints view. Nothing is served yet: shape what it should answer, then click Deploy to put it live at its URL.

See Deploy and URLs.