Learn / HDR BasicsHow to check if your screen supports HDR
A box that says "HDR" isn't proof of much. Here's what actually determines whether a display can show real HDR, and how to check yours directly instead of trusting the marketing.
"HDR" shows up on TV boxes, monitor spec sheets, and phone marketing pages so often that it stops meaning much on its own. Some of those claims are backed by real hardware capability. A lot of them are the bare minimum required to legally print the label. Here's how to actually find out what your specific display can do.
What actually determines real HDR capability
Three things matter more than the word "HDR" itself: peak brightness (how many nits the display can actually hit, at least in small highlight areas), contrast capability (can it get genuinely dark in the same frame it's showing something bright — this is where local dimming zones or per-pixel emission, as in OLED, matter enormously), and bit depth (enough levels to represent the wider range without visible banding — see What is bit depth?). A display can be technically HDR-certified while being weak on all three.
The VESA DisplayHDR certification tiers are a useful reference specifically because they're numbered by real requirement level — DisplayHDR 400 requires far less (400 nits peak, no local dimming mandate) than DisplayHDR 1000 or True Black tiers. "HDR" alone, without a tier or spec, tells you very little.
What a browser can actually check for you
A web page can ask the operating system, in real time, whether the current display is reporting HDR capability — using the CSS dynamic-range media feature (matchMedia('(dynamic-range: high)')). That's a genuine, live capability probe, not a guess based on your device model. What it can't do is measure your panel's actual peak nits or contrast ratio — the OS doesn't expose raw hardware specs like that to a browser, so no web-based tool, including this one, can report them directly.
Headroom's Compatibility Checker runs this and a full set of related probes (P3 and Rec.2020 gamut support, canvas HDR rendering, image decode/encode support) live in your browser and reports SUPPORTED, UNSUPPORTED, or honestly UNKNOWN when a probe genuinely can't be run — never a guess dressed up as a result.
Seeing it with your own eyes
Beyond what software can query, the most direct check is visual: does a genuine highlight actually look brighter than the surrounding white, not just more saturated? The Display Test generates a real nit-reference brightness ramp, grayscale and highlight-rolloff gradients, and gamut swatches — fresh, computed patterns, not a downloaded image — so you can judge directly whether your specific screen, in its current setting, is actually rendering extra range.
If the checks say yes but content still looks flat
That's usually not a display problem. Common causes: the browser tab or app isn't requesting HDR output even though the display supports it, an OS-level HDR toggle for that specific display is switched off, or the image itself doesn't actually carry HDR data despite looking like it should — see Inspect to check a specific file honestly rather than assuming.
Questions people actually ask
My monitor's box says 'HDR400' or similar — is that real HDR?
It's a real certification tier (VESA DisplayHDR), but the lowest ones are widely considered weak. DisplayHDR 400 only requires 400 nits peak brightness with no local dimming requirement, which is a modest step up from a good SDR display, not the kind of highlight punch HDR content is designed to show. Higher tiers (600, 1000, and up) with real local dimming get much closer to what HDR content actually needs.
Can software actually detect whether my display supports HDR?
Partially. A browser can query whether the OS and display are currently reporting HDR capability (via CSS's dynamic-range media feature) — that's a real, live check, not a guess. What it can't do is measure your display's actual peak brightness, contrast ratio, or whether it has real local dimming — the OS doesn't expose that, so no browser-based tool can either.
Why does a page say my display supports HDR but the image still looks the same as SDR?
A few common reasons: the specific app or browser tab isn't requesting HDR output even though the OS/display can support it, the OS's HDR toggle for that display is off, or the content itself doesn't have real HDR data despite being labeled that way. Each of those is a different failure point worth checking separately.
What's the single most reliable way to check?
Run an actual capability probe rather than reading a spec sheet — Headroom's Compatibility Checker queries your browser and OS directly, right now, and the Display Test shows real nit-reference and highlight-rolloff patterns so you can judge with your own eyes whether brighter really looks brighter.
