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Responsive Design - Step 1 of 5

Responsive Design | Cross-browser and device preview tool

Cross-browser and device preview tool

Free online web page checker across devices and browsers

Enter a URL above to preview it across devices

What This Tool Does

This free online tool lets you preview any web page simultaneously across multiple browsers and device sizes - desktop, tablet, and mobile - without needing to own or configure each device. Enter a URL and instantly see how it renders on Chrome at 1440px, an iPhone 15 Pro, a Galaxy S24, and more, all on one screen.

Why Responsiveness Matter

Different browsers render CSS differently, and mobile users now account for over half of global web traffic. A layout that looks perfect on your development machine may break on a 375px iPhone, show misaligned navigation on Firefox, or have unreadable font sizes on a tablet. Catching these issues before your users do protects both conversions and search rankings, since Google uses mobile-first indexing.

Key Optimization Checks

Navigation collapses correctly on mobile (hamburger menu visible and functional)
Touch targets are at least 44x44px - buttons and links easy to tap on small screens
No horizontal scrollbar appears at any viewport width (check 320px, 375px, 412px)
Font sizes remain readable - body text =16px on mobile, headings scale with clamp()
Images and media are fluid - no overflow, correct aspect ratio across all viewports
Core layout renders consistently across Chrome, Firefox, and Safari (flex/grid gaps, font rendering)

Pro Tip

Start every preview session at 375px - the iPhone SE viewport is the tightest real-world screen your visitors are likely to use, and if your layout holds there it will hold almost everywhere. Pay particular attention to your above-the-fold CTA: if a user has to scroll just to find your primary button on mobile, you are losing conversions before they even start. Once mobile looks solid, step up to 768px (tablet) and 1280px (desktop) and check that your grid expands gracefully rather than just stretching. Use the Analyze this view button to get an AI-generated punch-list of the specific issues most likely to affect each device - it saves the back-and-forth of manually hunting through DevTools.

Frequently asked questions

This free online tool lets you preview any web page simultaneously across multiple browsers and device sizes — desktop, tablet, and mobile — without needing to own or configure each device. Enter a URL and instantly see how it renders on Chrome at 1440px, an iPhone 15 Pro, a Galaxy S24, and more, all on one screen.
Many websites set an X-Frame-Options or Content-Security-Policy: frame-ancestors header that blocks them from being embedded inside an iframe. This is a security measure on the target site, not a fault with this tool. The AI analysis still works in these cases — it reasons about the URL and viewport size without needing to render the page.
Clicking "Analyze this view" sends the URL and device viewport details to the Claude AI API, which returns a concise, practical review of likely layout issues at that screen width — covering navigation collapse, touch target sizing, font scaling, browser-specific quirks, and specific things to manually check. You will need an Anthropic API key to use this feature.
API keys are available from console.anthropic.com. Create a free account, navigate to API Keys, and generate a new key. Your key is entered directly into this tool and is only ever sent to the Anthropic API — it is never stored on our servers.
The tool covers three categories. Desktop includes Chrome at 1440px, Firefox at 1280px, and Safari at 1920px. Tablet includes iPad Air (820px), iPad Mini (768px), and Surface Pro (912px). Mobile includes iPhone 15 Pro (393px), Pixel 8 (412px), iPhone SE (375px), and Galaxy S24 (360px). Use the "All" tab to see one representative from each category side by side.
The preview and layout tool is completely free with no account required. The AI analysis feature requires your own Anthropic API key, which has its own usage-based pricing from Anthropic. Typical analyses use a small number of tokens and cost a fraction of a cent per request.
Different browsers render CSS differently, and mobile users now account for over half of global web traffic. A layout that looks perfect on your development machine may break on a 375px iPhone, show misaligned navigation on Firefox, or have unreadable font sizes on a tablet. Catching these issues before your users do protects both conversions and search rankings, since Google uses mobile-first indexing.
Browser developer tools let you simulate one device at a time within a single browser engine, and they require access to the page's source code. This tool renders the live URL across multiple viewports simultaneously in one view, making it faster to spot cross-device inconsistencies at a glance — and the AI analysis layer surfaces likely issues even for sites you cannot inspect directly.
This tool is part of The Laughing Professor On Page SEO Toolbox, where multiple diagnostics and generators are combined into a single workflow for site optimization.

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