Browsers and Contexts

A descriptor overrides metrics, user agent and input flags inside a desktop engine. It reproduces no phone hardware, no shipping mobile browser and no mobile OS, so a green run proves your responsive layout works, not that iOS does.

Default to the bundled build: it is pinned to the Playwright version, reproducible everywhere and runs ahead of the stable browsers. Reach for a branded channel only where fidelity to the shipping product matters, and accept that it auto-updates.

Playwright's ignoreHTTPSErrors and bypassCSP are deliberate deviations from a real browser. Default both off, enable them only for the tests or environments that need it, and keep one path running with the real certificate and policy.

Almost everything Playwright drives. The page's own scripts never run, but navigation, clicks, filling fields, locators, assertions and Playwright's evaluate call all still work, because the driver talks to the browser over the protocol rather than through page script.

Rarely, and only for a capability no supported option provides. Playwright computes a default argument set and supports the browsers it ships; every custom flag or foreign binary is a divergence your team owns, debugs and revisits at each upgrade.

It stops at what the page can observe. Playwright's context options substitute the values and media-query state the browser reports, so the right code branch runs; they do not reproduce a real device, font stack or network.