Define a resource schema, get simulated REST endpoints, and run GET, POST, PUT, and DELETE requests against a live in-browser data store.
Create Resource
Schema Fields
Endpoints
Request Builder
Response
Data Store
Create a resource to get simulated REST endpoints with full CRUD operations and live state.
A mock API sandbox simulates a real REST API server — complete with stateful CRUD operations — without requiring any backend infrastructure. Define a resource (like "products" or "users"), specify its schema, and immediately get working GET, POST, PUT, and DELETE endpoints you can call and inspect.
Unlike static JSON mocks, RealJSON's sandbox maintains live state: a POST request actually adds a record, a DELETE actually removes it, and a subsequent GET reflects those changes. State is saved in your browser's localStorage so it persists across page reloads within the same browser session.
Static JSON mock files return the same response every time. They can't simulate what happens after a POST (does the new record appear in the next GET?), after a DELETE (does the list shrink?), or across multiple API calls in sequence. For testing multi-step workflows — user registration, cart management, order placement — you need a mock that actually maintains state.
AI agents that test applications face this problem acutely: an agent cannot host its own server. It needs a zero-config endpoint that behaves like a real API. This sandbox provides exactly that — a lightweight stateful backend that runs in the browser tab without any server, Docker container, or cloud account.
Build and test your frontend against realistic API behavior before the backend is ready. No more waiting for backend teams.
Let AI agents test multi-step flows — create a user, fetch them back, update them, delete them — against a real stateful endpoint.
Sketch out a resource schema and immediately see what the REST interface looks like before committing to an implementation.
Demonstrate REST API concepts with live create/read/update/delete operations without needing any infrastructure.
Define your expected data shapes and test that your code correctly handles list responses, single-record responses, 404s, and 201 creates.
To generate realistic seed data for your resources, use the Correlated JSON Generator. To test how your frontend handles edge cases in API responses, use the JSON Chaos Injector. To validate that your API responses conform to expected schemas, try the Constraint-Violation Sandbox.
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