ViewportLab Responsive Tester

ViewportLab Responsive Tester is a lightweight Chrome extension built for developers, designers, product teams, and website owners who need to quickly check how a web page behaves across different screen sizes. Instead of switching between multiple tools or manually resizing the browser window, ViewportLab opens a responsive device testing panel inside Chrome. You can test common mobile phones, tablets, and desktop viewport presets, switch between portrait and landscape orientation, adjust scale, and apply the simulated device mode to the current tab. ViewportLab is especially useful for early responsive QA, landing page review, mobile layout checks, product page testing, and quick visual inspection before publishing changes. Key Features Test responsive layouts in Chrome Use common mobile, tablet, and desktop device presets Switch between portrait and landscape orientation Adjust preview scale for different screen sizes Apply device simulation to the current active tab Avoid common iframe preview blocking by testing inside the real page context Use a clean side panel workflow without leaving the current page Supports English, Chinese, Japanese, Korean, French, and German Stores preferences locally in the browser No account, login, payment, or external API required Who It Is For Front-end developers checking responsive layouts Designers reviewing mobile and desktop page behavior Product managers testing landing pages and product pages SEO and marketing teams reviewing mobile page presentation Website owners who need quick layout checks before publishing Privacy Summary ViewportLab does not require an account and does not collect personal information. The extension does not upload browsing data, tested URLs, page content, or user preferences to a remote server. Settings such as selected language, theme, scale, and device preferences are stored locally in Chrome extension storage.