HDR test

What your browser reports

Any website can read these four values without asking, and each browser means something slightly different by them.

• dynamic-range In the standard, as MDN documents it, "high" means the screen and browser can show high brightness, high contrast and more than 8 bits per color, not that HDR is switched on. In Chromium's source, Chrome and Edge on Windows answer "high" only while Windows HDR is on for that screen. On a Mac they answer "high" when macOS says the screen can go brighter than white, except on an Intel Mac's built-in screen with 2x headroom or less.
• video-dynamic-range The same question, for video. On Windows, Mozilla says Firefox's answer follows whether the display is set to HDR, not whether it could be.
• color-gamut The widest standard gamut the screen roughly covers: sRGB, p3 or rec2020. Firefox answers sRGB on every screen, because it doesn't support wide-gamut color, according to MDN's compatibility data.
• Color depth In Chromium's code, Chrome reports 30 bits per pixel when it treats the screen as HDR and 24 when it does not.

No browser tells a website how bright your screen can get, so this test can't give you a figure in nits. Chrome has proposed a way to ask, listed on Chrome Platform Status, but it builds on a screen details feature that Firefox and Safari oppose, and Safari has said it would rather not share a screen's brightness headroom.

Highlights and wide color

If HDR output works, the 2x patch looks plainly brighter than White. The step where the patches stop getting brighter is roughly your screen's headroom at its current settings, and changing those settings moves it. On an external screen in Windows, Microsoft says, the SDR content brightness slider sets how bright the page's white is. Chromium's code takes headroom as the screen's peak over that white, so a brighter white leaves less of it.

On an LCD with full-array local dimming, light from a bright patch can spill into the dimmed zones around it, a halo DisplayNinja calls blooming. Light at the edges of a black screen is backlight bleed instead, which the backlight bleed test finds. RTINGS notes that an OLED reaches its peak only in small highlights, and that bright static elements raise its risk of burn-in, which the burn-in test checks.

In each color pair the left half is a Display P3 color and the right half the sRGB color with the same numbers. RTINGS' gamut tests found that many wide-gamut monitors stretch sRGB colors unless their sRGB mode is on. Then both halves look vivid and alike.

Turn on HDR in Windows and macOS

In Chrome and Edge the patches stay plain white until your computer sends HDR to the screen. Switch HDR on, then press Show again, and do the same after moving the window to another screen.

Windows 11

Start > Settings > System > Display. With more than one screen, pick the HDR one at the top, then turn on HDR. Laptops may switch HDR off on battery; the HDR page has a setting for that. A desktop duplicated across two screens gets no HDR, so choose Extend these displays.

macOS, external display

Apple menu > System Settings > Displays, select the display, then turn on High Dynamic Range. The switch appears only on third-party displays that support HDR10.

macOS, built-in display

There's no switch. On battery, the Optimize video streaming while on battery option under System Settings > Battery plays HDR video in SDR.

Browser support

Only Chrome and Edge can show the patches brighter than white. They need WebGPU's extended tone mapping, which MDN's data lists for those two alone. In any other browser the button still tries, and tells you why if it can't.

Versions from MDN's browser compatibility data, read in September 2026. Chrome 129 covers Windows, macOS and ChromeOS; Linux follows in 144, on Intel Gen12 or newer graphics only.

WebKit's Safari 26 release post says Safari shows HDR video from version 14 and HDR images from 26. Mozilla's release notes and graphics blog say Firefox plays HDR video on macOS and, from version 153, on Windows with HDR on, but shows no HDR images yet.

How the HDR test works

The test checks three media features and the screen's color depth when the page opens, and again whenever your browser reports a change. Nothing is sent anywhere, and no photo or video is loaded: every patch is generated on the page.

• The answer. Yes or No comes from dynamic-range, except in Firefox, where it comes from video-dynamic-range, whose meaning on Windows Mozilla has described.
• The highlights. White is the page's own white. Each patch beside it is a WebGPU canvas in 16-bit floating point with tone mapping set to extended. MDN's WebGPU reference says that setting lets values above 1.0 go past the page's white. Values are sRGB-coded, so twice the light is written as 1.35, not 2.
• The colors. CSS color(display-p3) beside the sRGB color with the same numbers. The test doesn't measure how much of each gamut your screen covers.
• What it can't see. It can't see black level or your screen's own tone mapping, and no browser reports brightness. The monitor test covers black level and gamma. Mozilla's graphics team notes that HDR needs at least 10 bits per color to match the quality of SDR, and the color banding test shows whether a gradient reaches your screen smooth.