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Game rules
One pot, many players. Every cent you deposit is a ticket, one ticket wins the whole pot, and your chance is your share. The house never plays: it takes a fee from the pot and nothing else. These are the rules enforced by the JustPoker game engine; where the table and this page could ever disagree, the engine's published tests are the reference.
Jackpot is one shared pot. Players deposit into it while a round is open, every cent buys one ticket, and when the entries close one ticket is drawn. Its owner is paid the whole pot less a 5% fee. The more you deposit, the larger your share of the tickets and the better your chance — but the prize is the same pot for everyone.
The house is never your opponent: it does not deposit and has nothing riding on the result. It takes the fee from every pot, whoever wins, so whatever your share, a deposit returns 95% of itself on average.
Each round is decided by a server seed committed when the round opens and a public randomness beacon round fixed only when its entries close, so nobody, us included, can know the winner while anyone can still deposit. You can check any finished round on our Provably Fair page.
Deposit $1 to $1,000. It is taken from your balance at once and becomes an entry: one ticket for every cent, numbered on from the tickets already in the pot. You may deposit up to 5 times a round, up to $2,500 in all.
While you are the only player the round stays open. You can withdraw your deposits, and they come back by themselves if nobody joins within 15 minutes.
The first deposit of a second player starts a 30-second countdown. It never stops and is never extended: anyone may deposit until it ends, up to 25 players and a pot of $25,000.
At zero the entries are locked: no more deposits, no withdrawals. The round's entries hash and its beacon round are published at once; drand publishes that round 3–6 seconds later.
The round's server seed and the beacon decide the winning ticket, and the wheel lands on it. Its owner is paid the whole pot less the 5% fee; every other entry is lost. The server seed is revealed.
The result is shown for 8 seconds, then a new round opens with a new server seed. A deposit that reaches us after entries closed is refused with nothing taken, and the table offers to deposit in the next round.
Set the amount with the chips, ½ and 2×; the button shows the chance your deposit would give you. When a round has closed it offers Deposit next round, and while you are alone in a round, Withdraw.
Deposits are whole cents. A deposit that would pass one of these caps is refused, and the table tells you how much room is left.
Chips of $1, $5, $10, $25, $100, $500, or type an amount.
In up to 5 deposits.
A full round takes deposits only from players already in it.
Deposits stop when the pot is full.
Every deposit is checked before it is taken
Every cent you deposit is one ticket. Tickets are numbered from 0 in the order of the deposits, so each deposit owns one unbroken range, and the winning ticket is drawn from all the tickets in the pot, each exactly as likely as any other. Your chance is your deposits divided by the pot.
Your chance falls as other players deposit, and it is final only when the entries close. The table shows it live, and the button shows what a deposit would make it.
Whatever your share, a deposit returns 95% of itself on average. In round 1 of the published vectors, alice deposits $5.00 of a $20.00 pot: a 25.00% chance of being paid $19.00, which is $4.75 on average — 95% of the deposit. A larger share wins more often, never more cheaply.
Three players, four entries: alice deposited twice, so they hold two ranges.
When the round is drawn the house takes 5% of the pot and the winner is paid the rest. Nothing else is taken, and the fee applies to the whole pot, so every player pays it in proportion to their deposits.
The fee is rounded down to the cent, so it is never more than 5%; the fraction of a cent goes to the winner. Deposits of $10.00 and $14.68 make a pot of $24.68; 5% of it is $1.234, so the fee is $1.23 and the winner is paid $23.45.
The fee is recorded with each round when it opens, so a change to it applies only to new rounds. Individual rounds swing widely: most deposits are lost, and a few win far more than they staked. Please read our responsible gambling information and set limits before you play.
| Round | Pot | Fee (5%) | Winner is paid |
|---|---|---|---|
| Two smallest deposits | $2.00 | $0.10 | $1.90 |
| Vector round 1 | $20.00 | $1.00 | $19.00 |
| Vector round 45 | $5,025.00 | $251.25 | $4,773.75 |
| A full pot | $25,000.00 | $1,250.00 | $23,750.00 |
Fee = 5% of the pot, rounded down to the cent. The winner is paid the pot less the fee.
A round with one player can always be undone, and every deposit in it is refunded. Once a second player has joined, the round is drawn and produces a winner, with two exceptions, in which every deposit is refunded instead: our staff cancel the round before its entries close, or a closed round cannot be drawn because its beacon round never arrives or because of a fault on our side. Both are described below.
Only if a closed round's beacon round still cannot be fetched 10 minutes after the close may our staff refund every deposit, and only if our server's own attempt to fetch it fails at that moment: if it succeeds, the round is drawn instead. Every such refund is shown publicly as “Refunded: randomness beacon unavailable” with its round number, and every one stays on our list of refunded games.
Before drawing, our server also checks that the entries it has recorded still give exactly the entries hash published at the close and the same tickets. If they do not, which only a fault on our side can cause, the round is never drawn: once 10 minutes have passed since the close our staff may refund every deposit, even though the beacon round has arrived. That refund is recorded with the problem found and the beacon value, and the round appears on the same list with its round number.
A round's winner needs inputs that nobody holds together before the close: a server seed committed when the round opens, the list of entries, and a beacon round that does not exist until seconds after the close.
seq:username:amount and joined with |. It pins the ticket table before the beacon value exists, so no entry can be moved afterwards.jackpot:number:round:randomness:entries hash followed by :0, :1, … Each result gives 5 numbers of 48 bits. The first one below the limit — 248 minus the remainder of 248 divided by the pot — is taken, and the winning ticket is its remainder after dividing by the pot. Skipping the few numbers above the limit makes every ticket exactly equally likely.Open any round in your hand history and choose Verify, or read the full scheme on the Provably Fair page.
The first published test vector, on a real drand quicknet round: the smaller player wins.
0fdef169ef108e2826cdb4d895a10ea3021edde33fb7dcc417bb007f97b1f8572e330b18c20d228aaa7153bc4f4cbb3e9169f6141cce385d72cdef370733a5b5b22aad4794f7451896f7a371aa46106fd84d919f3f569acd5b2fddf1d1440af37ab29860fc4e55f6cba8afc745af2a0b89ff7538d0245846da9bd5fb41b39c727ab29860fc4e, are 134,907,479,260,238, below the limit of 281,474,976,710,000 for a pot of 2,000 tickets: accepted.A test-only vector with a pot of 247 + 1 tickets, far beyond any real cap, chosen so that about half of all numbers lie above the limit.
The limit is 140,737,488,355,329. All 5 numbers of the first result are at or above it and are skipped:
The first number of the next result, 12,371,617,846,607, is below the limit, so the winning ticket is 12,371,617,846,607: alice's.
At real pots, of at most $25,000, a number is skipped less than once in 112,589,990 draws.
Any correct implementation must reproduce these winning tickets exactly. Round 1 uses a real drand round; the others use the development beacon.
| Round | Entries | Pot (tickets) | Beacon | Winning ticket | Winner |
|---|---|---|---|---|---|
| 1 | 2 | 2,000 | 1,000,000drand | 238 | alice |
| 2 | 4 | 6,000 | 32,689,930dev | 2,902 | carol |
| 3 | 3 | 3 | 32,690,100dev | 1 | bob |
| 45 | 6 | 502,500 | 33,000,500dev | 484,195 | erin |
| 7 | 2 | 140,737,488,355,329test only | 34,000,000dev | 12,371,617,846,607 | alice |
The verifier's Jackpot mode checks the commitment, the entries hash and the beacon round, and recomputes the winning ticket, the winner and the payout. Paste the values above to try it.
Node.js and its own crypto module, nothing of ours.
const { createHash, createHmac } = require("node:crypto");
function uniformInt(key, message, n) {
const N = BigInt(n), R = 2n ** 48n, limit = R - (R % N);
for (let i = 0; ; i++) {
const b = createHmac("sha256", key).update(`${message}:${i}`).digest();
for (let c = 0; c < 5; c++) {
const u = BigInt("0x" + b.subarray(c * 6, c * 6 + 6).toString("hex"));
if (u < limit) return Number(u % N);
}
}
}
const serverSeed = "3f9a1c8e6b2d4f7a9c0e1b3d5f7a9c2e4b6d8f0a1c3e5b7d9f1a3c5e7b9d0f2a";
const randomness = "b22aad4794f7451896f7a371aa46106fd84d919f3f569acd5b2fddf1d1440af3"; // drand quicknet round 1000000
const entries = "1:alice:500|2:bob:1500";
const entriesHash = createHash("sha256").update(entries).digest("hex");
console.log(uniformInt(serverSeed, `jackpot:1:1000000:${randomness}:${entriesHash}`, 2000)); // 238The randomness that decides a game comes from drand, a public randomness beacon run by the League of Entropy, a group of independent universities, companies and foundations. Its quicknet chain publishes a new value every 3 seconds. Each value is a threshold BLS signature produced jointly by the network's nodes: it is unique, nobody can compute it before enough nodes have signed, and anyone can check it against the chain's public key.
A game's beacon round is fixed at the moment the countdown ends and the entries close: our server takes the latest round published at that moment and adds 2. That round is published 3–6 seconds later. Until then it does not exist anywhere, so nobody — no player and not us — can know the result while anyone can still take part. The round number is shown the moment entries close, before its value exists.
Our server fetches the round from drand's public relays and checks its signature against the quicknet public key before using it; the relays only carry it. A round's randomness is the SHA-256 of its signature, and you can look up any round yourself, for example round 1,000,000, the one the worked example below uses.
The beacon round is counted from our server's clock, so our server also checks that clock against drand: while the games are in use it regularly fetches drand's newest round and checks its signature like any other. If drand has already published a round that, by our clock, is still more than a second away, our clock is behind real time, and joins and deposits stay closed until it is right again.
What remains to trust is that enough of the beacon's independent nodes do not conspire with us. Test servers use a predictable development beacon instead, always labelled “Development beacon (predictable; local testing only)”; it is never used on the live site.
You may hold one account only. Two accounts of one person in the same round gain nothing — together they are simply one larger share that pays the same fee — and multi-accounting is prohibited by our Terms. A last-second deposit buys tickets at the same price as any other, and the countdown never extends.
No. In Jackpot you play other players. We never create, join or deposit, and we take nothing but the fee from the pot, whoever wins.
And even if an account were ours — or someone inside our company who knows every server seed — it could not know the result: the beacon round that decides it is fixed only when entries close and published seconds later. Knowing the server seed is useless without it. That is why our staff need no rule against playing.
Because a bot would be the house playing against you. It would play with our money, so Jackpot would stop being a game between players: the house would become your opponent, with a different return and a reason to want you to lose. We keep the house out of it entirely.
If nobody else deposits, nothing is lost: withdraw whenever you like while you are alone, or every deposit is refunded after 15 minutes.
Jackpot has a chat room of its own. Signed-in players can post messages of up to 200 characters; messages are deleted after 30 days.
Chat and the lobby are public
Deposits from $1.00 to $1,000.00, a 5% fee on the pot. Your balance, limits and reality checks apply at Jackpot exactly as they do everywhere on JustPoker.
18+ only. Gambling can be harmful; play within limits you set in advance. Help is available through the organisations listed on our responsible gambling page.