Quick Answer
Provably fair gambling sites use cryptographic hashing to ensure that the outcome of the game was determined before you placed your bet, it is native to Bitcoin and not used by traditional online casinos, and you do not have to place your trust in the casino as you can verify the math yourself.
How Provably Fair Works — Step by Step
There are two concepts to this system: the server seed and the client seed. The outcome of the games are not determined by either the server or the client seed alone but by the two together.
1
Casino generates a server seed and hashes it
Before any spin in any game the casino will create a random server seed. They will then publish the cryptographic hash of the server seed to you. As long as they do not change the server seed, the cryptographic hash will not change either.
2
You provide your client seed
You will supply a client seed to the casino; most will automatically generate a client seed for you but you can change it to any value you would like. As the casino does not have access to your client seed, they cannot know the outcome of your spin.
3
The spin result is computed from both seeds
The outcome of each spin is calculated by combining the server seed, the client seed, and a nonce (a counter that increments with each bet place). The calculation is performed by a deterministic mathematical algorithm meaning the same input will always generate the same outcome.
4
After the spin, the casino reveals the server seed
After each bet is placed the casino will reveal the original server seed. You can use a free online tool to hash that value yourself and verify that the hash published to you prior to your bet matches the hash published after the bet is placed. If the hashes match, the casino created the server seed prior to your spin and could not have manipulated the outcome.
5
Recalculate the result yourself to verify
By knowing the server seed, the client seed, and the nonce the casino can calculate the outcome of the player's spin just as the casino did. If the calculated result matches the outcome paid to the player for that bet the game was provably fair.
ℹ️
You don't need to verify every spin. While you do not need to verify every spin that is made by the casino, you should have the ability to verify any spin if you would like. The existence of such a system and the act of verifying every spin is what ensures the fairness of the casino is not manipulated.
Provably Fair vs. RNG-Certified: What's the Difference?
Traditional online casinos use RNG software that is certified by third party testing and accreditation labs to ensure fairness. The provably fair system is different.
| Feature | RNG Certified | Provably Fair |
|---|---|---|
| Who verifies outcomes? | Third-party audit lab (you trust the lab) | You (directly, with math) |
| Can players verify individual spins? | No | Yes — every single one |
| Requires trust in casino? | Yes — after-the-fact audits | No — pre-committed cryptographic proof |
| Available on traditional casino games? | Yes (Pragmatic, NetEnt, etc.) | No — Bitcoin-native only |
| Manipulation technically possible? | Possible between audits (rare but theoretically) | Mathematically impossible if implemented correctly |
| Game variety | Thousands of titles | Smaller library (growing) |
⚠️
Not all casinos that claim "provably fair" actually implement it correctly. Not all casinos that advertise themselves as provably fair actually implement the system. Casinos must publish the hash of their server seed prior to your bet, reveal the server seed after your bet is placed, and provide tools for you to verify that their server seed was published before your bet was placed. Any casino that does not follow these steps is only utilizing the provably fair system as marketing copy.
How to Verify a Provably Fair Spin Yourself
- Open the fairness verification panelTo verify that any game is provably fair you will open the fairness verification panel for the game (usually located as a shield icon in the game) to view the server seed hash prior to starting to play.
- Note the server seed hashThe hash of the server seed is published to you prior to your game session and cannot be changed after you have placed your bets.
- Reveal the server seed after playingAfter you have finished playing the game you will click the "Reveal Server Seed" button within the game settings for the casino to reveal the original unhashed server seed.
- Run the seed through a SHA-256 toolYou will use a free online tool to hash the revealed server seed and compare that result to the hash revealed by the casino after your game session. If the hashes match the server seed was committed prior to your game session and the casino could not have manipulated your outcome.
- Confirm the hash matchesIf the output matches what was shown at the start, the seed was committed before your spin — no manipulation possible.
- Verify individual spin outcomesFor even further verification the casino also publishes a tool that allows players to input the raw server and client seeds to calculate the outcome of each player spin.
Key Facts at a Glance
SHA-256
Hash algorithm used by most PF systems
2009
Year provably fair was first introduced (Bitcoin-era)
0%
Chance of manipulation if correctly implemented