You can connect to Blast by instantiating a new ethers.js JsonRpcProvider object with a RPC URL of the Blast network.

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Mainnet

const ethers = require('ethers'); // ethers v6
const url = 'https://rpc.blast.io';
const provider = new ethers.JsonRpcProvider(url);
See Network Information for additional mainnet RPC endpoints.

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Testnet

const ethers = require('ethers'); // ethers v6
const url = 'https://sepolia.blast.io';
const provider = new ethers.JsonRpcProvider(url);