Inside the 20-second hand challenge.

Twenty seconds, one mechanic

The game is on purpose tiny. The entire interaction is: pinch your thumb to your index finger, then release. Cycle through that motion as fast as you can for 20 seconds. The total pinches the camera detected is your score. There are no secondary mechanics, no power-ups, no bonus modes. The narrowness is the design.

Why narrow? Because the game is trying to measure one thing — your sustained motor speed in a specific motion — and any added mechanic would muddy the number. The score has to mean what it says, or the leaderboard is meaningless.

What the camera sees

When you tap start, the browser asks for permission to use your camera. If you allow it, the page opens a video stream from your camera and starts running a hand-tracking model on each frame.

The model is trained to find a hand and identify a small set of landmark points on it — the wrist, the base and tip of each finger, the knuckles. The model returns those points, frame by frame, as the camera feeds new pictures in. The page never displays the camera feed at full size; it uses the landmark positions to drive the game.

What the page is mainly watching:

• The position of the thumb tip.
• The position of the index fingertip.
• The distance between those two points.

When that distance gets small — your thumb and index finger close together — the game registers a "closed" state. When the distance opens back up, the game registers a return to "open." A clean close-then-open cycle is one pinch. The counter ticks up by one.

What "counts" as a pinch

The tracker uses a threshold. The two fingertips have to come close enough that the system is confident the pinch was real, not just a partial motion. The threshold is set tight enough that lazy half-pinches don't slip through, but loose enough that you don't have to bury your fingertips together for it to register.

Three things will reliably not count:

• A pinch that closes partway and opens. The closure didn't pass the threshold; it doesn't add to your number.
• A pinch that closes and stays closed. The system needs the open-state return to register the next rep.
• A pinch the camera couldn't see clearly — out of frame, in shadow, against a backlit silhouette.

This is where lighting and framing earn or cost you reps. The motion can be perfect, but if the camera couldn't see it, it didn't happen — at least as far as the score is concerned.

Why the video stays on your device

The hand-tracking model is a piece of code that runs inside your browser. When the page loads, the model loads with it. Each new camera frame goes through the model right there in the page. The model spits out the landmark points. The page uses those points to update the score.

At no point does a video frame, an image, or any pixel from your camera go out over the network. The only network requests the game makes are for game data — loading the page itself, fetching the leaderboard, and submitting your final score at the end. Camera content stays where it started: in front of the camera.

This isn't a privacy promise made for marketing reasons. It's a structural property of how the game is built. There's no upload endpoint for camera frames because there's no need for one. The score is generated locally and only the score is shared.

Light and framing

Most of the variance between people's scores in their first three runs is technique, not reflex. Specifically: light and framing.

Light

The model needs to be able to identify your fingers clearly. Daylight from a window, or any normal indoor light source positioned roughly in front of you, will do the job. A backlit silhouette (a window behind you, you in the foreground) gives the model a dark blob and washes out the finger details it needs. Heavy shadow on one side of the hand is also rough.

Framing

Hold your hand at roughly the distance you'd hold a book to read it. Too close and your hand fills the frame and the model loses context. Too far and the fingertips are tiny and the small distance changes between open and closed are hard to read.

The other hand

If you're playing on a phone, you'll usually hold the phone with one hand and pinch with the other. The model is generally fine with two hands in frame, but it will sometimes try to track the wrong one. If the count seems wrong, try moving the non-pinching hand out of the camera's view.

The countdown

After you tap start and allow the camera, you get a 3-2-1 countdown before the 20-second clock begins. This is intentional — the model needs a moment to acquire your hand and settle on tracking, and your hand needs a moment to settle into a comfortable pose. Pinches done during the countdown do not count toward the score.

The instant the countdown ends, the timer starts and the green go-state appears. The instant the timer hits zero, the count locks. The score on screen at that moment is the score that goes to the board.

The score

At the end of the run, the page does three things:

• Locks the final count.
• Submits the number to the leaderboard along with a placeholder display name (you can edit it after).
• Renders the result screen with your row highlighted and the rows above and below for context.

From there, you can tap into your row, type a real name, and the row updates. Your name is also saved locally so it's prefilled next time.

Anti-abuse, briefly

The score that lands on the board passes through a server-side check that rejects obvious nonsense. A claim of 4,000 pinches in 20 seconds will not be accepted; it's physically impossible and the server says so. The game also rate-limits rapid duplicate submissions from the same session.

Beyond that, the underlying defense is that the score is hard to fake. It's bottlenecked by physical hand speed in a real 20-second window, in front of a real camera. There's no auto-clicker shortcut because there's no clicking. Trying to spoof the camera with a video of someone else pinching ends up with the model tracking a hand that isn't yours and the score being whatever that recording produces — which is not, in practice, an advantage.

If you want to climb the board

The mechanic is small enough that, after a few runs, you've seen all of it. The work after that is technique. The most concentrated version of the technique work is in the tips article. The mechanical limit of your hand is real, but it's almost never what's holding back your number.