Provably fair is a way of running an online game of chance so that you can check the result yourself, with math, instead of trusting the site's word. Before you open a box or a case, the site locks in its secret answer and shows you a scrambled fingerprint of it. After you play, it reveals the secret, and anyone can recompute the outcome to prove it was set in advance and never changed. That is the whole promise: not "trust us," but "check us."
This guide explains what provably fair means in plain language, how the check actually works, where it applies in the mystery box and case opening world, and, just as importantly, what it does not prove. By the end you will be able to verify a real result yourself, on your own device, in under a minute.
What provably fair actually means
A normal online game asks you to trust that its random number generator was not rigged and its outcome not edited after the fact. You usually cannot check either. Provably fair replaces that trust with proof. The site commits to its secret in advance in a way it cannot later change, and gives you everything you need to reproduce the outcome afterward. If your recomputation matches what the site showed, the result is honest. If it does not, you have caught a problem, with evidence.
The word "provably" is the important part. It is not a marketing badge or a certificate hanging on the wall. It is a claim that you, personally, can prove or disprove a specific result using public inputs and a standard hash function. A site that says it is provably fair but does not let you reproduce a result is not provably fair. It is just using the phrase.
The sealed envelope: commit and reveal
The mechanism behind every provably fair system is commit-then-reveal, and the simplest picture is a sealed envelope.
Before you play, the site writes its secret number on a card, seals it in an envelope, and hands you a tamper-proof stamp of that envelope. You cannot read the card, but you hold proof it exists and has not been swapped. You play. Afterward, the site opens the envelope and shows you the card. You confirm the card matches the stamp you were given at the start. Because the stamp was in your hands before you played, the site could not have changed the card to fix your result.
In technical terms, the card is the server seed, a long random string. The stamp is a SHA-256 hash of that seed, a one-way fingerprint that is easy to produce from the seed but effectively impossible to reverse. You get the hash up front and the real seed after, and the two must match. That single property, committed before and revealed after, is what makes the whole thing checkable.
The three inputs behind your pull
A provably fair outcome is not decided by the site alone. It comes from three inputs combined and run through a hash:
- The server seed. The site's secret, committed in advance as a hash and revealed after your seeds rotate. Learn the detail in what is a server seed.
- The client seed. Your input, tied to your account and changeable at any time. Because your seed is part of the recipe, the site cannot aim a specific item at you.
- The nonce. A play count that increases by one with each pull, so every opening in a sequence produces a different result.
These get fed into HMAC, a standard keyed-hash function, and the output hex is turned into a number that maps to your item. HMAC sounds technical, but for your purposes it is just a well-tested blender: put the same three ingredients in and you always get the same result out, and change any ingredient by one character and the result changes completely. That determinism is exactly what lets you re-run the calculation and check it.
How to verify a result yourself
Here is the part that matters. You do not have to understand the cryptography to use it. You just need four values from a completed pull, and a tool that recomputes the outcome. The verifier below does the math on your own device, and nothing you paste is sent to any server.
- Before you play, save the hashed server seed. This is the fingerprint, the stamp on the envelope.
- Note your client seed and the play count for the pull you want to check.
- Rotate your seed. Switching to a new server seed forces the site to reveal the old, real one in your history.
- Paste all four values into the verifier. It recomputes the outcome and confirms the revealed server seed matches the hash you saved.
If the recomputed result matches what the site showed, and the revealed seed matches the original fingerprint, the result was committed before you played and was not altered. That is a real proof, done by you, not a promise from the site.
Step 1Where did you play?
Using Ripster box / upgrade: HMAC-SHA256 over clientSeed:noncedetails
HMAC-SHA256 keyed with the server seed over clientSeed:nonce. The first 8 hex characters become a 32-bit integer, divided by 2^32 and multiplied by 100 for a roll in [0, 100). Items are sorted by item ID and selected by cumulative probability: the first item whose cumulative probability is at least the roll wins.
Where to find your numbers on Ripster.gg:
- Before rolling, copy the Server Seed Hash from the Provably Fair modal (also recorded per roll in Account History).
- After the roll, open the Provably Fair modal to copy the Server Seed, Client Seed and Nonce.
- Change your Client Seed anytime in Account Settings; doing so reveals the current Server Seed so all past rolls become verifiable.
Source: Ripster.gg's own fairness page
Step 2Paste your numbers
Runs entirely on your device via your browser's built-in cryptography. Don't take our word for it: open DevTools → Network, click the button, and watch: zero requests.
Runs entirely in your browser. Nothing you paste is sent anywhere.
Where provably fair shows up: mystery boxes and cases
Most explanations of provably fair are written for crypto dice and crash games, but the same system runs underneath a large part of the mystery box and case opening world. Sites like these publish a drop table for each box, listing every possible item and its probability, and then use a provably fair draw to pick which one you get. Many map the hashed outcome to a ticket number in a fixed range, for example 1 to 1,000,000, and the item whose published ticket range contains your number is the one you win.
That last step, turning a hash into a specific item rather than just a number, is what makes box verification a little different from casino verification, and more useful. When a site publishes both its algorithm and its ticket ranges, you can check not only that the draw was honest but that the exact item you received was the correct one for your roll. That is the strongest form of the check, and it is available on more box sites than most players realise.
Provably fair versus a normal RNG certificate
You will also see sites advertise that their random number generator is certified by an independent testing lab. This is a real and useful thing, but it answers a different question. An RNG certificate says a lab tested the site's randomness at some point and found it sound. You cannot re-run that test, and it does not cover your specific result. Provably fair is the opposite: it does not rely on a lab, and it lets you check your own individual outcome, right now, yourself. The two can coexist, and the strongest sites offer both, but only provably fair puts the proof in your hands.
What provably fair does not prove
This is where honest guidance matters, and where most explanations stop short. A provably fair check is powerful but narrow. It proves one thing: that a completed result was generated from the values committed before your play and was not changed afterward. It does not promise anything else about a site.
Keeping that boundary clear is not a knock on provably fair. It is what makes the claim credible. A tool that told you a site was completely safe because one roll verified would be lying to you. A tool that tells you exactly what it proved, and no more, is one you can rely on.
Verification, not prediction
One more thing worth stating plainly, because scams cluster here. Provably fair lets you verify a result that already happened. It cannot predict a result that has not. The server seed is committed as a hash before your client seed is even applied, so nothing, and no one, can know your next outcome in advance. Any tool, service, or seller promising to predict a pull, guarantee a win, or reveal the next drop is either mistaken or a scam. The only honest use of these inputs is checking the past, never forecasting the future.
The bottom line
Provably fair turns "trust the site" into "check the site." It commits the site to a secret before you play, reveals it after, and hands you the math to reproduce any result. On a mystery box or case site, that means you can confirm both that your draw was honest and, where ticket ranges are published, that the item you got was the right one. It does not promise a site is solvent, well run, or paying out, and a good verifier will always tell you so. Used with that boundary in mind, it is the single most useful trust signal in this space, and the one thing you never have to take on faith.