docs-third-party-add-gelato-vrf

arbitrum-docs/for-devs/third-party-docs/Gelato/gelato-vrf.md

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+---
+title: "Getting Started with Gelato VRF"
+description: "Learn how to use Gelato VRF"
+author: anirudhmakhana
+sme: anirudhmakhana
+sidebar_label: "Gelato VRF"
+---
+
+# What is Gelato VRF?
+
+Gelato VRF offers real randomness for blockchain applications on Arbitrum by leveraging Drand, a trusted decentralized source for random numbers. With Gelato VRF, developers on Arbitrum get random values that are both genuine and can be checked for authenticity. Explore Gelato VRF's support for all supported networks [here](https://docs.gelato.network/web3-services/vrf/supported-networks).
+
+## Applications of Gelato VRF
+
+The potential applications of a reliable and transparent random number generator on the blockchain are vast. Here are just a few use cases:
+
+- Gaming and Gambling: Determine fair outcomes for online games or decentralized gambling applications.
+- Decentralized Finance (DeFi): Use in protocols where random selections, like lottery systems, are required.
+- NFT Generation: Randomly generate traits or characteristics for unique digital assets.
+- Protocol Decision Making: In protocols where decisions need to be randomized, such as selecting validators or jurors.
+
+# How does Gelato VRF work?
+
+Gelato VRF (Verifiable Random Function) provides trustable randomness on EVM-compatible blockchains. Here's a brief overview:
+
+Core Components:
+
+- Drand: Gelato VRF utilizes Drand, a decentralized randomness beacon ensuring unpredictability and unbiased randomness.
+
+Top-level Flow:
+
+- Contract Deployment: Use GelatoVRFConsumerBase.sol as an interface for requesting random numbers.
+- Requesting Randomness: Emit the RequestedRandomness event to signal the need for a random number.
+- Processing: Web3 functions fetch the random number from Drand.
+- Delivery: The fulfillRandomness function delivers the random number to the requesting contract.
+
+# Quick start guide
+
+In order to get your VRF up and running with Gelato, you need to make your contract VRF Compatible.
+
+## Step 1: Setup your development environment
+
+Ensure you have either [Foundry](https://book.getfoundry.sh/getting-started/installation) or [Hardhat](https://hardhat.org/) set up in your development environment.
+
+## Step 2: Install the Gelato VRF contracts
+
+- For hardhat users:
+
+```shell
+ npm install --save-dev @gelatodigital/vrf-contracts
+```
+
+- For Foundry users:
+
+```shell
+ forge install gelatodigital/vrf-contracts --no-commit
+```
+
+## Step 3: Inherit `GelatoVRFConsumerBase` in your contract
+
+```solidity
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.18;
+
+import {GelatoVRFConsumerBase} from "./GelatoVRFConsumerBase.sol";
+
+contract YourContract is GelatoVRFConsumerBase {
+    // Your contract's code goes here
+}
+```
+
+## Step 4: Request randomness
+
+```solidity
+function requestRandomness(bytes memory data) external {
+        require(msg.sender == ...);
+        uint64 requestId = _requestRandomness(data);
+    }
+```
+
+Step 5: Implement the `fulfillRandomness` function
+
+```solidity
+ function _fulfillRandomness(
+        bytes32 randomness,
+        uint64 requestId,
+        bytes memory data,
+    ) internal override {
+    }
+}
+```
+
+## Step 6: Pass dedicated msg.sender
+
+When you're ready to deploy your Gelato VRF-compatible contract, an important step is to include the dedicated `msg.sender` as a constructor parameter. This ensures your contract is set up to work with the correct operator to fulfill the randomness requests. It's crucial to ensure that only authorized requests are processed.
+
+```solidity
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.18;
+
+import {GelatoVRFConsumerBase} from "./GelatoVRFConsumerBase.sol";
+
+contract YourContract is GelatoVRFConsumerBase {
+    constructor(address operator)
+        GelatoVRFConsumerBase(operator) {
+        // Additional initializations
+    }
+
+    // The rest of your contract code
+}
+```
+
+Once your contract is ready & deployed, grab the address and [Deploy your VRF instance](https://docs.gelato.network/web3-services/vrf/quick-start/deploying-your-vrf-instance)!