The Mint Close Authority Extension

The MintCloseAuthority extension is a Mint extension that allows the authority to close and retrieve the rent from a Mint account that has a current supply of 0.

This extension is useful for cleaning up unused mints and reclaiming the SOL that was used to pay for the account's rent exemption. The mint can only be closed when no tokens are in circulation.

Initializing the Mint Account

To initialie the MintCloseAuthority extension on a Mint account we're going to need the initializeMintCloseAuthority() function.

Here's how to create a mint with the Mint Close extension:

import {
    Keypair,
    SystemProgram,
    Transaction,
    sendAndConfirmTransaction,
} from '@solana/web3.js';
import {
    createInitializeMintInstruction,
    createInitializeMintCloseAuthorityInstruction,
    getMintLen,
    ExtensionType,
    TOKEN_2022_PROGRAM_ID,
} from '@solana/spl-token';
 
const mint = Keypair.generate();
 
// Calculate the size needed for a Mint account with Transfer Fee extension
const mintLen = getMintLen([ExtensionType.MintCloseAuthority]);
 
// Calculate minimum lamports required for rent exemption
const lamports = await connection.getMinimumBalanceForRentExemption(mintLen);
 
// Create the account with the correct size and owner
const createAccountInstruction = SystemProgram.createAccount({
    fromPubkey: keypair.publicKey,
    newAccountPubkey: mint.publicKey,
    space: mintLen,
    lamports,
    programId: TOKEN_2022_PROGRAM_ID,
});
 
// Initialize the Mint Close Authority extension
const initializeMintCloseAuthority = createInitializeMintCloseAuthorityInstruction(
    mint.publicKey,
    keypair.publicKey,
    TOKEN_2022_PROGRAM_ID,
);
 
// Initialize the mint itself
const initializeMintInstruction = createInitializeMintInstruction(
    mint.publicKey,
    6,
    keypair.publicKey,
    null,
    TOKEN_2022_PROGRAM_ID,
);
 
// Combine all instructions in the correct order
const transaction = new Transaction().add(
    createAccountInstruction,
    initializeMintCloseAuthority,
    initializeMintInstruction,
);
 
const signature = await sendAndConfirmTransaction(connection, transaction, [keypair, mint]);
 
console.log(`Mint created! Check out your TX here: https://explorer.solana.com/tx/${signature}?cluster=devnet`);

Closing the Mint Account

If a Mint account has a supply of zero, the CloseMint Authority can reclaim the rent on that account by usingin the closeAccount instruction like so:

const closeMintInstruction = createCloseAccountInstruction(
    mint.publicKey,
    keypair.publicKey,
    keypair.publicKey,
    [],
    TOKEN_2022_PROGRAM_ID,
);
 
const transaction = new Transaction().add(closeMintInstruction);
 
const signature = await sendAndConfirmTransaction(connection, transaction, [keypair], {skipPreflight: false});
 
console.log(`Mint closed! Check out your TX here: https://explorer.solana.com/tx/${signature}?cluster=devnet`);

Token2022 with Web3.js

The Mint Close Authority Extension

Initializing the Mint Account

Closing the Mint Account