Verifiable randomness on Arc.

Quickstart

npm i @d20dao/vrf-sdk

// SPDX-License-Identifier: MIT
pragma solidity 0.8.28;
import {D20VRFConsumer} from "@d20dao/vrf-sdk/contracts/D20VRFConsumer.sol";
import {ID20VRF} from "@d20dao/vrf-sdk/contracts/interfaces/ID20VRF.sol";

contract Dice is D20VRFConsumer {
    mapping(uint256 => bytes32) public results;

    constructor(address coordinator) D20VRFConsumer(coordinator) {}

    function roll(bytes32 seed) external payable returns (uint256 id) {
        id = ID20VRF(vrfCoordinator).requestRandomness{value: msg.value}(seed, 100_000, msg.sender);
    }

    function _fulfillRandomness(uint256 id, bytes32 word) internal override {
        results[id] = word;
    }
}

Pass the coordinator below to the constructor and send at least quoteFee(100_000) with roll.

Coordinator

Arc Mainnet · 5042

0xd20da057469C45928912d983F45790C41e290571 · manifest

Arc Testnet · 5042002

0xd20DA0FF9087d053f0291524Eac12abA1ADBd945 · manifest

Fee and delivery

Fee

max(0.02 USDC, 3 × base fee × (300,000 + callback gas))

Delivery

Measured median 2 seconds for an isolated request on Arc Testnet.

Refund

If a request is not fulfilled within 60 seconds, its fee can be refunded to the request's refund address.

Verification

Each 200-block epoch commits one drand round for paid demand; a VRF proof binds a future block. Anyone can replay a result from public data. Full trust model

Questions

How do I get a random number on Arc?

Extend D20VRFConsumer with the coordinator 0xd20da057469C45928912d983F45790C41e290571, pay the quoted fee in USDC and call requestRandomness. The random word arrives in _fulfillRandomness.

What does it cost?

max(0.02 USDC, 3 × base fee × (300,000 + callback gas)), paid in native USDC by the requesting transaction. Read quoteFee(callbackGasLimit) from the coordinator; the owner sets pricing for future requests.

Can the result be verified?

Yes. Each epoch's drand round is verified onchain and each result carries a VRF proof. The Explorer and the SDK replay a request from public chain data.

Is there a testnet?

Yes. Arc Testnet, chain 5042002, coordinator 0xd20DA0FF9087d053f0291524Eac12abA1ADBd945.

What if a request is not fulfilled?

If a request is not fulfilled within 60 seconds, its fee can be refunded to the request's refund address.

Why not use block.prevrandao?

On Arc, block.prevrandao always returns 0, so it carries no randomness.