MockResponse

Build against production-quality APIs before they exist.

Install realistic backend systems with persistent state, relationships and failure simulation.

Stop mocking JSON.
Start simulating systems.

Traditional mocks return responses. MockResponse simulates systems.

Stateful

Every request changes the backend. Reads reflect earlier writes.

  1. POST /customers201 Created
  2. GET /customers1 customer
  3. DELETE /customers/c_1204
  4. GET /customersempty

Connected

Resources reference each other, and relationships stay intact.

  • Customercus_1
  • Subscriptioncustomer: cus_1
  • Invoicesubscription: sub_1
  • Paymentinvoice: inv_1

Realistic

Production doesn't always return 200. Inject the failure modes your code will eventually hit — before production does.

429 Rate limited500 Server error401 UnauthorizedTimeoutLatency

Inject failures per endpoint or per backend — on the Nth call, at a failure rate, conditionally, or after elapsed time.

Install complete backend systems

Don't build mocks endpoint-by-endpoint. Install realistic APIs with data, relationships and workflows already configured.

241 providers · 131,018 ready-made mock endpoints

Import OpenAPI. Get a backend.

Simple. Clear. From spec to callable, persistent backend in one flow — with AI seeding realistic, connected data along the way.

AI where it helps. Not where it hurts.

The API stays deterministic — AI only generates the data behind it.

  • Generate datasets
  • Create realistic organisations
  • Expand schemas
  • Seed relationships

Your backend evolves.
Instead of static JSON.

Every request changes what the next request sees — just like a real system.

  1. POST /users201 Created

    A new user is stored

  2. GET /usersReturns the new user

    State persists across calls

  3. DELETE /usersUser disappears

    Mutations update the store

  4. GET /ordersRelationships update automatically

    Connected resources stay consistent

Frequently asked questions

Everything you need to know before spinning up your first backend emulator. Can't find your answer? Talk to us.

Stop waiting for backend APIs.
Install one instead.