Why this exists
I needed to flip a coin with a friend remotely. I googled it and every result was pretty much trash: ads everywhere, ugly, no live-sync, nothing you could verify. So I went on a mission to build the best coin flip on the internet.
No accounts, emails, or ads. One link, modern UI, enjoyable features, and a result you can verify yourself. Play a best of 3 or 5, let friends watch along, throw in a reaction when it lands, and swap sides for the rematch.
Jan Morte Procházka · github.com/JanProchy
Guides
Why nobody can rig the flip
The result is locked in before anyone flips, and after the match you can check it yourself.
- Sealed before round 1The room picks a secret and shows you only its fingerprint.
- You both add a seedEach browser adds a random seed of its own. Nobody sees the secret.
- All three make the faceThe face comes from all three at once — change any one and it could land the other way.
- Opened and checkedAfter the match the envelope opens: the secret inside matches its fingerprint, and your browser can redo the same mix and get the same face.
For the curious: the fingerprint is SHA-256 of the server seed; each face is HMAC-SHA256(server seed, “host seed:guest seed:round”), first hex digit even = Heads. Checked on a million flips: 50.09% Heads, 49.91% Tails. Verify a flip yourself.
Flip a coin online: questions answered
How do I flip a coin online with friends?
Open coinflip.now, tap Invite to play and send the link. When your friend opens it, you both tap Ready. One coin flips and you both see it land at the same moment. No app, no account.
Does everyone really see the same result at the same time?
Yes. The server decides the flip and when it starts, so every screen lands within about a tenth of a second. It’s one coin, not a separate toss on each phone.
Is the coin flip fair and random?
Yes, and you can check it. Before the first flip the room seals a fingerprint of the server’s secret, both browsers add a seed of their own, and the secret is revealed after the match. Anyone can recompute every result on the verify page.
Do I need an account, signup, or app?
No. No signup, no install, no ads. Open the page and send the link.
Can people watch without playing?
Yes. Send the watch link and anyone can follow live and react. Watchers can’t touch the result.
Can I use it for choices other than heads or tails?
Sure. Type what Heads and Tails stand for, say Pizza and Salad, and the result shows your words.
Is it free, and how long does a room last?
Free, no limits. A room stays open while you play, and closes a minute after everyone leaves or after 30 minutes idle. A new one takes a second.
Know someone who'd use a fair coin?