Provably Fair Prize Draws on Base: How ThePrize Picks Winners On-Chain
"Provably fair" gets used loosely across the internet. For most sites it means trust us, we have a certificate. At ThePrize, it means something narrower and much stronger: for competitions drawn on-chain, the random number that decides the winner is generated by a public smart contract on Base, and anyone — entrant or not — can check it without asking our permission.
This post explains what that actually involves, in plain English.
The problem with ordinary prize draws
A traditional prize draw asks you to trust three invisible things:
- that the draw actually happened,
- that every valid entry was in the hat,
- that nobody re-ran the draw until a convenient name came out.
Even honest operators can't easily prove any of that. The draw happens on a private machine, the "random" number is known only to the operator, and the evidence is whatever they choose to publish.
What ThePrize does differently
ThePrize runs its on-chain draws through a dedicated smart contract on Base (the Ethereum Layer-2), using Chainlink VRF v2.5 as the randomness source. The flow looks like this:
- A competition is registered on the contract with its name, total ticket count, and the number of winners.
- That same transaction requests randomness from Chainlink VRF — a decentralised oracle network, not a ThePrize server.
- Chainlink returns the random words in a fulfilment transaction, and the contract derives the winning ticket number(s) from them.
- The draw transaction hash is published on the competition's proof panel, linking straight to BaseScan.
The contract doing this work is public: ThePrizeVRF at 0x640e042fB04DD1b8d5E9B36642D325976F0C4cDD on Base. You can open it on BaseScan right now and read every draw it has ever performed.
Because the randomness comes from Chainlink VRF, it arrives with a cryptographic proof that is verified on-chain before the contract will accept it. Nobody — not ThePrize, not Chainlink, not the Base sequencer — can substitute a different number after the fact. If you want the deeper mechanics of why that's true, we've written a separate plain-English guide: How Chainlink VRF proves a prize draw was fair.
How to verify a draw yourself
You don't need any special tools — just a block explorer:
- Open the finished competition page on ThePrize and go to its Proof section.
- Follow the draw transaction link to BaseScan.
- Confirm the transaction interacted with the ThePrizeVRF contract (
0x640e…C4cDD). - Check the fulfilment: the random words and the resulting winning ticket number(s) are readable on-chain.
- Compare the winning ticket number with the published winner on the site.
That's the whole point of the phrase provably fair — the proof is a public artefact, not a promise.
What about entries — could the "hat" itself be rigged?
Fair randomness only matters if the pool of tickets is honest too. Ticket numbers on ThePrize are assigned sequentially as entries are made, every entry list is visible on the competition page, and paid entries settle in USDC on Base, so purchases have their own on-chain footprint.
ThePrize also operates as a skill-based prize competition with a free entry route: every competition requires a correct answer to a skill question, and every competition can be entered free by post, with postal entries validated and entered on equal terms with paid ones. (That structure — skill question plus free entry route — is what places ThePrize outside UK gambling regulation, per UK legal opinion. Details are in our terms and conditions.)
The honest caveats
A few things we'd rather say plainly than let you discover in the small print:
- "Provably fair" applies to draws performed through the VRF contract. That's how ThePrize draws are designed to run — each such draw carries its BaseScan-verifiable transaction on its proof panel. A draw without a published VRF transaction should be judged on exactly that basis.
- The blockchain proves the number was fair. Prize fulfilment — shipping a physical prize, crediting USDC — is an off-chain human process, which is why payouts publish their own transaction links where applicable.
- Randomness means exactly that: entering does not guarantee winning, and no strategy improves a random draw.
Why Base?
Base is a low-fee Ethereum Layer-2 with mature Chainlink support. Low fees matter for a prize platform: they make it economical to put every draw on-chain rather than reserving the transparency budget for headline events. And because Base settles to Ethereum, the draw record inherits Ethereum's durability — the proof doesn't disappear when a marketing page gets redesigned.
ThePrize is an 18+ skill-based prize competition platform. No purchase is necessary — every competition has a free postal entry route entered on equal terms. Please play responsibly: gamcare.org.uk.