Fullscreen API Tester
Test the Fullscreen API, check support and toggle full-screen mode from your browser.
How to use this tool
- Open this page — it runs instantly in your browser, no signup or install.
- Allow any permission prompt if asked; everything stays on your device.
- Use the on-screen controls — results update live.
Test the Fullscreen API, check support and toggle full-screen mode from your browser.
How it works
The Fullscreen API Tester checks whether your browser supports the standard Fullscreen API and provides a button to toggle fullscreen mode on the page. When fullscreen is active, the page expands to fill the entire display with no browser chrome visible.
The tool displays the current fullscreen support status, shows which vendor-prefixed version of the API (if any) your browser uses, and confirms whether the toggle action succeeded. This is useful for web developers building fullscreen experiences such as games, presentations, or media players, and for users who want to understand their browser's fullscreen capabilities.
Exiting fullscreen works by pressing the Escape key or clicking the Exit Fullscreen button. The tool listens to the fullscreenchange event and updates its status indicator in real time.
Fullscreen is supported in all major modern browsers. The main cause of failure in supported browsers is that the toggle was not initiated by a direct user gesture.
Worked example
Confirm fullscreen works and measure the available screen area
- Open the Fullscreen Tester.
- Click 'Enter Fullscreen'.
- Note the screen dimensions reported in fullscreen mode.
- Press Escape to exit.
- Compare the fullscreen dimensions to the windowed dimensions.
Confirmed fullscreen is supported and observed the exact pixel dimensions available in fullscreen versus windowed mode.
Common mistakes to avoid
- Expecting fullscreen to work when triggered without a user click — browsers require an explicit user gesture for security reasons.
- Forgetting that the browser's built-in fullscreen (F11) is different from the Fullscreen API — they behave similarly but are controlled separately.
- Assuming fullscreen hides all OS UI; some OSes keep the taskbar or dock visible depending on user settings.
Key terms
- Fullscreen API
- A browser API that allows a page or element to expand to fill the entire screen, hiding browser toolbars and the OS taskbar.
- fullscreenchange event
- A browser event that fires when the document enters or exits fullscreen mode, allowing scripts to react to the state change.
- Vendor prefix
- A browser-specific prefix (like webkit- or moz-) added to experimental APIs before they were standardised.
Frequently asked questions
- Why does fullscreen not work?
- Browsers require a user gesture (click) to enter fullscreen. It also cannot be triggered on load or from an iframe without the allow='fullscreen' attribute.
- How do I exit fullscreen with the keyboard?
- Press Escape to exit fullscreen in all browsers.