Provably Fair Calculator: Verify Any Casino Bet Yourself
A free provably fair verification tool that checks SHA-256 hashes and HMAC-SHA256 game results. Paste any casino's seeds and see the math for yourself — all computation runs in your browser.
On this page
How Provably Fair Verification Works
1. Before a bet, the operator commits to a server seed by publishing its SHA-256 hash.
2. The player provides (or receives) a client seed and a nonce that increments with each bet.
3. After the bet, the server seed is revealed. You hash it and compare to the committed hash — if they match, the operator didn't change the seed after seeing your bet.
4. The game result is derived from HMAC-SHA256(server_seed, client_seed:nonce), so both parties influence the outcome.
The derivation method (how the hex output maps to a game result) varies by game and operator. This calculator uses a simple dice-style conversion: first 8 hex chars → integer → mod 10001 → divide by 100 → result between 0.00 and 100.00.
🔒 All verification runs in your browser. No seeds are sent to any server.
The short answer
The tool above takes a server seed, its hash, a client seed, and a nonce — and runs the same cryptographic verification that a provably fair casino uses internally. It checks whether the server seed was committed honestly (the hash matches) and derives the game result from the combined seeds. Everything runs in your browser — no data is sent anywhere.
Key takeaway: Provably fair doesn't mean "trust the casino." It means you can verify every bet independently using standard cryptography. This calculator shows you exactly how that verification works — step by step, with the actual hash values visible.
How to use the calculator
- Get the seeds from your casino. After a bet resolves, provably fair casinos reveal the server seed, the original hash, the client seed, and the nonce. Copy all four values.
- Paste them into the calculator. Each field maps to one of the four values.
- Click Verify. The calculator runs two checks:
- Hash verification: Is `SHA-256(server_seed) == server_seed_hash`? If yes, the casino committed to the seed before you placed your bet.
- Result derivation: What does `HMAC-SHA256(server_seed, client_seed:nonce)` produce? This is the raw output that determines the game result.
- Compare the derived result to what the casino showed you. If they match, the bet was fair.
Don't have seeds handy? Click "Load Example" to see a working verification with pre-filled values.
How provably fair verification works
The system relies on cryptographic commitment — the casino proves it didn't change the outcome after you made your decision.
Before your bet:
- The casino generates a server seed and publishes its SHA-256 hash. This is a one-way function: you can check the hash later, but you can't reverse it to find the seed.
- You provide (or the casino generates) a client seed. Combined with a nonce (bet counter), these three values together determine the outcome.
After your bet:
- The casino reveals the actual server seed. You can now verify that `SHA-256(revealed_seed)` matches the hash you were shown earlier.
- You can independently compute `HMAC-SHA256(server_seed, client_seed:nonce)` and derive the game result.
If the hash matches and the derived result matches what was displayed, the casino couldn't have manipulated the outcome. The commitment was locked before you played.
For a full walkthrough of the cryptography, see our guide on how provably fair works. The seeds, nonces, and hashes lesson explains each component in detail, and the verify a bet yourself lesson walks through a real verification step by step.
Why verify at all?
Because trust is earned, not assumed. A casino that claims provably fair but doesn't let you verify is no different from one that simply says "trust us." The verification is the whole point — it replaces blind trust with mathematical proof.
Our article on how to verify a provably fair result covers the practical side. The certified RNG vs provably fair lesson explains how this compares to traditional casino fairness testing.
Important notes
- This is a generic educational tool. It implements standard SHA-256 and HMAC-SHA256 verification. Different casinos may use different algorithms to derive game results from the HMAC output — the hash verification step is universal, but the result derivation varies.
- All computation runs locally in your browser using the Web Crypto API. No seeds, hashes, or personal data are sent to any server.
- This tool does not connect to any casino. You paste the values manually and verify them independently.
What should I learn next?
- Provably Fair, Explained: Full guide to how the system works
- How to Verify a Result Yourself: Practical verification walkthrough
- Seeds, Nonces, and Hashes: The cryptographic building blocks
- Provably Fair & Casino Trust Course: The full structured course
- How to Tell if a Crypto Casino Is Legit: The broader trust checklist
About the author
Trust & Responsible Play Writer
Marcus focuses on judging casinos before you deposit — licensing checks, red flags, scam patterns — and the bankroll habits and limit tools that keep play under control.