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Chrome extensions

Introduction​

note

Extensions only work in Chromium when launched with a persistent context. Use custom browser args at your own risk, as some of them may break Playwright functionality.

Google Chrome and Microsoft Edge removed the command-line flags needed to side-load extensions, so use Chromium that comes bundled with Playwright.

The snippet below retrieves the service worker of a Manifest v3 extension whose source is located in ./my-extension.

Note the use of the chromium channel that allows to run extensions in headless mode. Alternatively, you can launch the browser in headed mode.

from playwright.sync_api import sync_playwright, Playwright

path_to_extension = "./my-extension"
user_data_dir = "/tmp/test-user-data-dir"


def run(playwright: Playwright):
    context = playwright.chromium.launch_persistent_context(
        user_data_dir,
        channel="chromium",
        args=[
            f"--disable-extensions-except={path_to_extension}",
            f"--load-extension={path_to_extension}",
        ],
    )
    if len(context.service_workers) == 0:
        service_worker = context.wait_for_event('serviceworker')
    else:
        service_worker = context.service_workers[0]

    # Test the service worker as you would any other worker.
    context.close()


with sync_playwright() as playwright:
    run(playwright)

Service worker idle suspension (MV3)​

Chrome MV3 service workers are automatically suspended after ~30 seconds of inactivity and restarted on demand. When this happens, Playwright keeps the same Worker object alive — no new 'serviceworker' event is emitted. New evaluate() calls issued during the restart window are stalled until the new context is ready and then resume automatically:

sw = context.wait_for_event('serviceworker')

# ... SW suspends after 30 s of inactivity and is restarted by the browser ...

# The existing handle is transparent across the restart.
sw.evaluate("sendMessage({ type: 'ping' })")  # just works
note

evaluate() calls that were already in-flight at the exact moment of suspension will throw with "Service worker restarted", matching the behaviour of page navigations mid-flight.

Testing​

To have the extension loaded when running tests you can use a test fixture to set the context. You can also dynamically retrieve the extension id and use it to load and test the popup page for example.

Note the use of the chromium channel that allows to run extensions in headless mode. Alternatively, you can launch the browser in headed mode.

First, add fixtures that will load the extension:

conftest.py
from typing import Generator
from pathlib import Path
from playwright.sync_api import Playwright, BrowserContext
import pytest


@pytest.fixture()
def context(playwright: Playwright) -> Generator[BrowserContext, None, None]:
    path_to_extension = Path(__file__).parent.joinpath("my-extension")
    context = playwright.chromium.launch_persistent_context(
        "",
        channel="chromium",
        args=[
            f"--disable-extensions-except={path_to_extension}",
            f"--load-extension={path_to_extension}",
        ],
    )
    yield context
    context.close()


@pytest.fixture()
def extension_id(context) -> Generator[str, None, None]:
    # for manifest v3:
    service_worker = context.service_workers[0]
    if not service_worker:
        service_worker = context.wait_for_event("serviceworker")

    extension_id = service_worker.url.split("/")[2]
    yield extension_id

Then use these fixtures in a test:

test_foo.py
from playwright.sync_api import expect, Page


def test_example_test(page: Page) -> None:
    page.goto("https://example.com")
    expect(page.locator("body")).to_contain_text("Changed by my-extension")


def test_popup_page(page: Page, extension_id: str) -> None:
    page.goto(f"chrome-extension://{extension_id}/popup.html")
    expect(page.locator("body")).to_have_text("my-extension popup")