Does FastAPI Work With Cypress?
FastAPI and Cypress work together seamlessly—FastAPI serves your API, Cypress tests your frontend against it.
Quick Facts
How FastAPI Works With Cypress
FastAPI and Cypress are complementary tools in a full-stack testing strategy. FastAPI runs your backend API server (typically on `http://localhost:8000`), while Cypress runs in the browser making requests to that API and testing frontend behavior. There's no direct integration layer needed—Cypress simply makes HTTP requests to your FastAPI endpoints using `cy.request()` or through your frontend application code. Your development workflow typically involves running `uvicorn main:app --reload` in one terminal and `cypress open` in another. Since FastAPI auto-generates OpenAPI/Swagger documentation and has built-in CORS support, configuring it to accept requests from Cypress (running on a different port) is straightforward. The main architectural consideration is ensuring your development FastAPI instance is accessible from Cypress, which usually means binding to `0.0.0.0` and allowing the appropriate CORS origin.
Best Use Cases
FastAPI Backend + Cypress Test Setup
pip install fastapi uvicorn python-multipart && npm install cypress --save-dev// FastAPI backend (main.py)
from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware
app = FastAPI()
app.add_middleware(
CORSMiddleware,
allow_origins=["http://localhost:3000"],
allow_credentials=True,
allow_methods=["*"],
allow_headers=["*"],
)
@app.get("/api/items")
async def get_items():
return [{"id": 1, "name": "Test Item"}]
// Cypress test (cypress/e2e/api.cy.ts)
describe('FastAPI Integration', () => {
it('fetches items from FastAPI', () => {
cy.request('GET', 'http://localhost:8000/api/items')
.should((response) => {
expect(response.status).to.eq(200);
expect(response.body).to.have.length(1);
expect(response.body[0].name).to.eq('Test Item');
});
});
});Known Issues & Gotchas
CORS errors when Cypress tries to make cross-origin requests to FastAPI
Fix: Enable CORS in FastAPI using `CORSMiddleware` with `allow_origins=["http://localhost:3000"]` (or your frontend dev server port)
Cypress runs in the browser sandbox and cannot directly access FastAPI logs or database state for assertions
Fix: Create FastAPI helper endpoints (e.g., `/test/reset-db`) that Cypress calls to set up test data, or use API requests to query state
FastAPI's async nature can cause race conditions if Cypress makes rapid sequential requests without proper waits
Fix: Use Cypress `cy.intercept()` to wait for network responses, or add explicit waits between API calls in your tests
Port binding conflicts when running FastAPI and frontend dev server simultaneously
Fix: Configure FastAPI on port 8000 and frontend on 3000+ to avoid collisions, or use Docker containers
Alternatives
- •Django REST Framework + Cypress: More mature backend with built-in admin panel, heavier than FastAPI
- •Node.js Express + Cypress: Keep entire stack in JavaScript/TypeScript for more unified development experience
- •FastAPI + Playwright: Python-based end-to-end testing if you want the same language for backend and tests
Resources
Related Compatibility Guides
Explore more compatibility guides