Does Flask Work With Playwright?
Flask and Playwright work together seamlessly—use Flask to build your web app and Playwright to test it end-to-end across browsers.
Quick Facts
How Flask Works With Playwright
Flask and Playwright are complementary tools designed to work independently but integrate naturally in a testing workflow. You build your Flask application normally, then use Playwright in your test suite to automate browser interactions against a running Flask server. Playwright handles launching browsers (Chromium, Firefox, WebKit), navigating to your Flask app's local URL, and simulating user interactions—all with excellent cross-browser support.
The typical architecture is straightforward: run your Flask development server on localhost in a test fixture, then point Playwright at that URL. Most developers use pytest as the test runner, with fixtures that start/stop the Flask server before each test. Playwright's async API pairs well with async Flask patterns, though the synchronous API also works fine. The main consideration is port management—ensure your test Flask instance doesn't conflict with other services, and properly clean up browser instances after tests complete.
This combination is particularly powerful because you test your Flask app in real browsers with JavaScript execution, network conditions, and rendering behavior—something unit tests alone cannot do. There's no special integration needed; they just work together through HTTP requests.
Best Use Cases
Quick Setup
pip install flask playwright pytest pytest-asyncioimport pytest
from flask import Flask
from playwright.sync_api import sync_playwright
@pytest.fixture
def app():
app = Flask(__name__)
@app.route('/')
def index():
return '<h1>Hello</h1><button id="btn">Click</button>'
return app
@pytest.fixture
def server(app):
server = app.run(port=5555, debug=False, use_reloader=False)
yield
server.shutdown()
def test_flask_with_playwright(server):
with sync_playwright() as p:
browser = p.chromium.launch()
page = browser.new_page()
page.goto('http://localhost:5555')
assert page.locator('h1').inner_text() == 'Hello'
page.click('#btn')
browser.close()Known Issues & Gotchas
Playwright may connect to Flask before the server is fully ready, causing immediate test failures
Fix: Add a small wait/retry loop or use pytest fixtures that properly wait for the server to bind before running tests
Port conflicts when running parallel tests—multiple Flask instances compete for the same localhost port
Fix: Use dynamic port assignment (port=0) or pytest-xdist with separate port ranges per worker
Playwright browser processes consume significant memory; running many parallel browser instances can exhaust system resources
Fix: Use browser context reuse, limit concurrent tests, or run Playwright tests in a separate CI stage with dedicated hardware
CORS or same-origin policy issues when testing across different Flask domains in a single test
Fix: Ensure Flask is configured with appropriate CORS headers or use Playwright's context isolation properly
Alternatives
- •Selenium + Flask: More mature than Playwright with broader language support, but slower and heavier
- •Cypress + Flask: Excellent DX for frontend testing, but requires JavaScript/Node.js knowledge and only supports Chromium-based browsers
- •Pupeteer + Flask: Lightweight headless Chrome automation, but limited to Chromium and lacks multi-browser native support
Resources
Related Compatibility Guides
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