Summary

• SOL is the name of Solana's native token. Each SOL is made from 1 billion Lamports.
• Accounts store tokens, NFTs, programs, and data. For now, we'll focus on accounts that store SOL.
• Addresses point to accounts on the Solana network. Anyone can read the data at a given address. Most addresses are also public keys.

Lesson

Accounts

All data on Solana is stored in accounts. Accounts can store:

• SOL
• Other tokens, like USDC
• NFTs
• Programs, like the film review program we make in this course!
• Program data, like a film review for the program above!

SOL

SOL is Solana's 'native token' - this means SOL is used to pay transaction fees, rent for accounts, and other common. SOL is sometimes shown with the ◎ symbol. Each SOL is made from 1 billion Lamports.

In the same way that finance apps typically do math in cents (for USD) and pence (for GBP), Solana apps typically transfer, spend, store, and handle SOL as Lamports, only converting to full SOL to display to users.

Addresses

Addresses uniquely identify accounts. Addresses are often shown as base-58 encoded strings like dDCQNnDmNbFVi8cQhKAgXhyhXeJ625tvwsunRyRc7c8. Most addresses on Solana are also public keys. As mentioned in the previous chapter, whoever controls the matching secret key for an address controls the account - for example, the person with the secret key can send tokens from the account.

Reading from the Solana Blockchain

Installation

We use an npm package called @solana/web3.js to do most of the work with Solana. We'll also install TypeScript and esrun, so we can run .ts files on the command line:

npm install typescript @solana/web3.js@1 esrun

Connect to the Network

Every interaction with the Solana network using @solana/web3.js is going to happen through a Connection object. The Connection object establishes a connection with a specific Solana network, called a 'cluster'. For now, we'll use the Devnet cluster rather than Mainnet. Devnet is designed for developer use and testing, and DevNet tokens don't have real value.

import { Connection, clusterApiUrl } from "@solana/web3.js";
 
const connection = new Connection(clusterApiUrl("devnet"));
console.log(`✅ Connected!`);

Running this TypeScript (npx esrun example.ts) shows:

✅ Connected!

Read from the Network

To read the balance of an account:

import { Connection, PublicKey, clusterApiUrl } from "@solana/web3.js";
 
const connection = new Connection(clusterApiUrl("devnet"));
const address = new PublicKey("CenYq6bDRB7p73EjsPEpiYN7uveyPUTdXkDkgUduboaN");
const balance = await connection.getBalance(address);
 
console.log(`The balance of the account at ${address} is ${balance} lamports`);
console.log(`✅ Finished!`);

The balance returned is in *lamports, as discussed earlier. Web3.js provides the constant LAMPORTS_PER_SOL for showing Lamports as SOL:

import {
  Connection,
  PublicKey,
  clusterApiUrl,
  LAMPORTS_PER_SOL,
} from "@solana/web3.js";
 
const connection = new Connection(clusterApiUrl("devnet"));
const address = new PublicKey("CenYq6bDRB7p73EjsPEpiYN7uveyPUTdXkDkgUduboaN");
const balance = await connection.getBalance(address);
const balanceInSol = balance / LAMPORTS_PER_SOL;
 
console.log(`The balance of the account at ${address} is ${balanceInSol} SOL`);
console.log(`✅ Finished!`);

Running npx esrun example.ts will show something like:

The balance of the account at CenYq6bDRB7p73EjsPEpiYN7uveyPUTdXkDkgUduboaN is 0.00114144 SOL
✅ Finished!

...and just like that, we are reading data from the Solana blockchain!

Lab

Let's practice what we've learned, and check the balance at a particular address.

Load a keypair

Remember the public key from the previous chapter.

Make a new file called check-balance.ts, substituting your public key for <your public key>.

The script loads the public key, connects to DevNet, and checks the balance:

import { Connection, LAMPORTS_PER_SOL, PublicKey } from "@solana/web3.js";
 
const publicKey = new PublicKey("<your public key>");
 
const connection = new Connection("https://api.devnet.solana.com", "confirmed");
 
const balanceInLamports = await connection.getBalance(publicKey);
 
const balanceInSOL = balanceInLamports / LAMPORTS_PER_SOL;
 
console.log(
  `💰 Finished! The balance for the wallet at address ${publicKey} is ${balanceInSOL}!`,
);

Save this to a file, and npx esrun check-balance.ts. You should see something like:

💰 Finished! The balance for the wallet at address 31ZdXAvhRQyzLC2L97PC6Lnf2yWgHhQUKKYoUo9MLQF5 is 0!

Get Devnet SOL

In Devnet you can get free SOL to develop with. Think of Devnet SOL like board game money - it looks like it has value, but it doesn't have value.

Get some Devnet SOL and use the public key of your keypair as the address.

Pick any amount of SOL you like.

Check your balance

Re-run the script. You should see your balance updated:

💰 Finished! The balance for the wallet at address 31ZdXAvhRQyzLC2L97PC6Lnf2yWgHhQUKKYoUo9MLQF5 is 0.5!

Check other student's balances

You can modify the script to check balances on any wallet.

import { Connection, LAMPORTS_PER_SOL, PublicKey } from "@solana/web3.js";
 
const suppliedPublicKey = process.argv[2];
if (!suppliedPublicKey) {
  throw new Error("Provide a public key to check the balance of!");
}
 
const connection = new Connection("https://api.devnet.solana.com", "confirmed");
 
const publicKey = new PublicKey(suppliedPublicKey);
 
const balanceInLamports = await connection.getBalance(publicKey);
 
const balanceInSOL = balanceInLamports / LAMPORTS_PER_SOL;
 
console.log(
  `✅ Finished! The balance for the wallet at address ${publicKey} is ${balanceInSOL}!`,
);

Swap wallet addresses with your classmates in the chat and check their balances.

% npx esrun check-balance.ts (some wallet address)
✅ Finished! The balance for the wallet at address 31ZdXAvhRQyzLC2L97PC6Lnf2yWgHhQUKKYoUo9MLQF5 is 3!

And check a few of your classmate's balances.

Challenge

Modify the script as follows:

• Add instructions to handle invalid wallet addresses.
• Modify the script to connect to mainNet and look up some famous Solana wallets. Try toly.sol, shaq.sol or mccann.sol.

We'll transfer SOL in the next lesson!