Real-time photosensitivity protection for the whole web.
NeuroShield is a Chrome extension that watches videos, canvases and animations on every website and hides content that flashes faster than WCAG 2.3.1 allows, usually within a fraction of a second. It's built for people with photosensitive epilepsy, migraine and visual snow.
Around 3% of people with epilepsy have seizures triggered by flashing light, more than a billion people live with migraine, and visual snow affects 2–3% of the population. Most flash-protection tools only cover a single site. Flashing content shows up everywhere: in social feeds, news, ads and games.
- Hides flashing as it happens. Every frame a video shows is measured against the WCAG 2.3.1 general and red flash thresholds. When the limit is crossed, the video is blacked out and paused.
- Lets you decide what happens next. Show dimmed lowers contrast so that even black-to-white flashing stays below the WCAG threshold. Show anyway reveals it, and NeuroShield starts watching again 10 seconds later.
- Covers more than videos. It checks canvases (games, HTML5 ads, WebGL) and short, repeating CSS animations, and it finds players inside shadow DOM and cross-origin frames.
- Gives you a panic button. Alt+Shift+H (or the popup) pauses every video and animation and covers the page instantly.
- Respects your choices. Settings apply to open tabs immediately, you can pause it per site, and it tells you when a video can't be scanned (cross-origin or DRM-protected) instead of guessing.
- Shows you it works. NeuroShield stays silent until something flashes. To check it, open its settings and press Run test: a strobe plays off screen, so nothing flashes on yours, and you see how fast it was caught and the card you'd see.
- Stays out of the way. All analysis runs on your device. It does next to nothing while nothing is playing, and its UI is isolated from page styles and works over fullscreen video.
| Level | Hides | Good for |
|---|---|---|
| Low | More than 5 flashes per second | Only intense strobing |
| Medium (default) | More than 3 flashes per second | The WCAG 2.3.1 limit |
| High | More than 2 flashes per second | Migraine, visual snow |
| Maximum | Any flash | Maximum caution |
Red flashes (changes to and from saturated red, the pattern behind the 1997 Pokémon incident) are counted too, even when brightness barely changes, and are treated as high risk.
Get NeuroShield from the Chrome Web Store. It updates automatically.
To run it from source:
git clone https://github.com/OMARVII/Neuroshield.gitOpen chrome://extensions, turn on Developer mode, choose Load unpacked and select the cloned folder. There's no build step.
- Find what can flash. The content script runs in every frame. It finds
<video>elements, large canvases and short repeating animations, including inside open and closed shadow roots and in custom elements that upgrade later. - Read every frame cheaply. Each presented video frame is uploaded into an sRGB texture. The GPU averages it down to 32×32 in linear light, and the result comes back through an asynchronous readback, so the page never waits (about 0.2 ms per 1080p frame). Canvases are read through
captureStream(). Machines without GPU acceleration use a 2D-canvas fallback. - Count flashes like WCAG does. Relative luminance (sRGB linearization, BT.709) is tracked for the whole frame and for 16 regions, so a flash in one corner isn't averaged away. Transitions are measured peak to peak, so smooth or ramped flashes count as fully as hard cuts. Red flashes use the WCAG saturated-red definition.
- Protect, then ask. The element is hidden with an inline filter that stays aligned while you scroll, and a card explains what happened.
On a 1080p60 video, NeuroShield 1.1 uses about 40% less main-thread time than 1.0 while analysing five times as many frames (every frame instead of ~12 per second). See docs/how-it-works.md for the details, measurements and known limits.
NeuroShield collects nothing, sends nothing and makes no network requests. Frames are reduced to 32×32 samples in memory and discarded. Settings, paused sites and a local count of hidden flashes stay in Chrome's local storage on your device. See PRIVACY.md.
| Permission | Why |
|---|---|
| Read and change data on all websites | Run the flash detector on every page, including tabs that were already open when NeuroShield was installed or updated. |
storage |
Remember your settings. |
scripting |
Start protection in tabs that were open before installation, without a reload. |
NeuroShield lowers exposure. It can't promise to catch everything, and it is not a medical device.
- Detection needs to see a few flashes first: about 0.3 seconds for fast strobing and up to a second near the threshold.
- Cross-origin videos without CORS, and DRM-protected streams (Netflix and similar), can't be read by any extension. NeuroShield shows a small notice and can dim them automatically.
- Reversing patterns (a checkerboard or stripes swapping black and white) aren't detected, because their average brightness doesn't change. At High and Maximum, fast motion can occasionally be taken for flashing.
- Animated GIF/WebP images and flashing done by scripts changing page colors aren't analyzed yet. Use Alt+Shift+H if something gets through, and please report it.
Requires Node 22+.
npm install
npx playwright install chromium # once, for the end-to-end tests
npm run lint # ESLint
npm run test:unit # detector, settings and tab-state unit tests (Node test runner)
npm run test:e2e # loads the extension into Chromium and plays real flashing videos
npm run build # dist/neuroshield-<version>.zip for the Chrome Web Store
npm run bench # main-thread cost on a 1080p60 video (needs ffmpeg)The end-to-end suite covers detection of every fixture (including 12 Hz, red/blue and smooth flashes), shadow DOM, iframes, fullscreen, strict CSP pages, live settings changes, the popup and the background worker. The detection tests run twice: once with WebGL and once with the 2D fallback.
src/
├── shared/settings.js settings shared by every context
├── content/ runs in every frame
│ ├── detector.js WCAG flash analysis (pure, unit-tested)
│ ├── sampler.js WebGL / 2D frame readback
│ ├── guards.js per-element protection (video, canvas, animation)
│ ├── overlay.js on-page UI (top layer + closed shadow root)
│ └── content.js discovery, settings, reporting
├── background/ service worker: toolbar, per-tab state, install
├── popup/ toolbar popup
├── options/ settings and welcome page
└── ui/tokens.css shared design tokens (light and dark)
test/unit/ Node unit tests
test/e2e/ Playwright tests, test pages and video fixtures
scripts/ build, icons, screenshots, fixtures, benchmark
Contributions are welcome. NeuroShield makes safety decisions, so detection changes need tests that show the before and after. See CONTRIBUTING.md.
MIT © Omar Khaled