Skip to content
Cardano Client Lib Cardano Client Lib

Minting an NFT

An NFT on Cardano is a native token with a quantity of 1, whose policy can’t mint any more. In this tutorial you’ll create that policy, describe the token with CIP-25 metadata, mint it on the Preview testnet and find it in your wallet.

Before you start, follow Your first transaction to create an account, fund it from the faucet and get a Blockfrost project id. To use a local network instead, see Test locally with Yaci DevKit. The dependencies are cardano-client-lib and cardano-client-backend-blockfrost.

The code reads your settings from the environment:

Terminal window
export BF_PROJECT_ID=<your Blockfrost Preview project id>
export TUTORIAL_MNEMONIC="<your 24 words>"

Step 1: Create the policy

Section titled “Step 1: Create the policy”

A token’s policy decides who can mint it and when. A policy id is the hash of its script, so a new script gives you a new policy.

long deadline = backend.getBlockService().getLatestBlock().getValue().getSlot() + 3600;
Keys policyKeys = KeyGenUtil.generateKey();
ScriptAll policyScript = new ScriptAll()
        .addScript(ScriptPubkey.create(policyKeys.getVkey()))
        .addScript(new RequireTimeBefore(deadline));
Policy policy = new Policy(policyScript, List.of(policyKeys.getSkey()));

ScriptAll means both conditions must hold: the new key signs, and the transaction is valid only before deadline. One slot is one second on Preview, so that’s one hour from now.

This is what makes the token one of a kind. A quantity of 1 alone doesn’t: without the deadline, the key holder could mint the same token again.

Step 2: Describe the token

Section titled “Step 2: Describe the token”

Wallets and explorers read an NFT’s name and image from CIP-25 metadata, which you attach to the minting transaction.

Asset nftAsset = new Asset("MyFirstNft", BigInteger.ONE);
NFT nft = NFT.create()
        .assetName(nftAsset.getName())
        .name("My First NFT")
        .image("ipfs://QmYwAPJzv5CZsnA625s3Xf2nemtYgPpHdWEz79ojWnPbdG")
        .description("Minted with Cardano Client Lib");
NFTMetadata metadata = NFTMetadata.create().addNFT(policy.getPolicyId(), nft);

Replace image with the location of your own file. This sample points to a placeholder on IPFS.

Step 3: Mint

Section titled “Step 3: Mint”
Tx tx = new Tx()
        .mintAssets(policy.getPolicyScript(), nftAsset, minter.baseAddress())
        .attachMetadata(metadata)
        .from(minter.baseAddress());


TxResult result = new QuickTxBuilder(backend)
        .compose(tx)
        .validTo(deadline)
        .withSigner(SignerProviders.signerFrom(minter))
        .withSigner(SignerProviders.signerFrom(policy))
        .completeAndWait(Duration.ofMinutes(5));
  • validTo(deadline) is required. The script accepts a transaction only if it declares that it expires before the deadline.
  • There are two signers: your account pays the fee, and the policy key authorizes the mint.
  • completeAndWait stops waiting after its timeout and then reports the status TIMEOUT, even though the transaction may still land. That’s why the complete code below checks for TxStatus.CONFIRMED.

Step 4: Find your NFT

Section titled “Step 4: Find your NFT”

A token’s unit is its policy id followed by its hex-encoded name. Ask the backend which UTxO at your address holds it:

String unit = AssetUtil.getUnit(policy.getPolicyId(), nftAsset);
holding = backend.getUtxoService().getUtxos(minter.baseAddress(), unit, 1, 1).getValue();

The complete code retries this for up to a minute, because a backend’s UTxO view can lag behind a confirmed transaction.

Run it

Section titled “Run it”
MintNft.java 
package tutorial;


import com.bloxbean.cardano.client.account.Account;
import com.bloxbean.cardano.client.api.model.Amount;
import com.bloxbean.cardano.client.api.util.AssetUtil;
import com.bloxbean.cardano.client.api.model.Utxo;
import com.bloxbean.cardano.client.backend.api.BackendService;
import com.bloxbean.cardano.client.backend.blockfrost.common.Constants;
import com.bloxbean.cardano.client.backend.blockfrost.service.BFBackendService;
import com.bloxbean.cardano.client.cip.cip25.NFT;
import com.bloxbean.cardano.client.cip.cip25.NFTMetadata;
import com.bloxbean.cardano.client.common.model.Networks;
import com.bloxbean.cardano.client.crypto.KeyGenUtil;
import com.bloxbean.cardano.client.crypto.Keys;
import com.bloxbean.cardano.client.function.helper.SignerProviders;
import com.bloxbean.cardano.client.quicktx.QuickTxBuilder;
import com.bloxbean.cardano.client.quicktx.Tx;
import com.bloxbean.cardano.client.quicktx.TxResult;
import com.bloxbean.cardano.client.quicktx.TxStatus;
import com.bloxbean.cardano.client.transaction.spec.Asset;
import com.bloxbean.cardano.client.transaction.spec.Policy;
import com.bloxbean.cardano.client.transaction.spec.script.RequireTimeBefore;
import com.bloxbean.cardano.client.transaction.spec.script.ScriptAll;
import com.bloxbean.cardano.client.transaction.spec.script.ScriptPubkey;


import java.math.BigInteger;
import java.time.Duration;
import java.util.List;


public class MintNft {


    public static void main(String[] args) throws Exception {
        BackendService backend = new BFBackendService(
                Constants.BLOCKFROST_PREVIEW_URL, System.getenv("BF_PROJECT_ID"));
        Account minter = Account.createFromMnemonic(Networks.preview(), System.getenv("TUTORIAL_MNEMONIC"));


        mint(backend, minter);
    }


    public static void mint(BackendService backend, Account minter) throws Exception {
        // 1. The policy: this key must sign, and only before the deadline
        long deadline = backend.getBlockService().getLatestBlock().getValue().getSlot() + 3600;
        Keys policyKeys = KeyGenUtil.generateKey();
        ScriptAll policyScript = new ScriptAll()
                .addScript(ScriptPubkey.create(policyKeys.getVkey()))
                .addScript(new RequireTimeBefore(deadline));
        Policy policy = new Policy(policyScript, List.of(policyKeys.getSkey()));


        // 2. The token and its CIP-25 metadata
        Asset nftAsset = new Asset("MyFirstNft", BigInteger.ONE);
        NFT nft = NFT.create()
                .assetName(nftAsset.getName())
                .name("My First NFT")
                .image("ipfs://QmYwAPJzv5CZsnA625s3Xf2nemtYgPpHdWEz79ojWnPbdG")
                .description("Minted with Cardano Client Lib");
        NFTMetadata metadata = NFTMetadata.create().addNFT(policy.getPolicyId(), nft);


        // 3. The transaction
        Tx tx = new Tx()
                .mintAssets(policy.getPolicyScript(), nftAsset, minter.baseAddress())
                .attachMetadata(metadata)
                .from(minter.baseAddress());


        TxResult result = new QuickTxBuilder(backend)
                .compose(tx)
                .validTo(deadline)
                .withSigner(SignerProviders.signerFrom(minter))
                .withSigner(SignerProviders.signerFrom(policy))
                .completeAndWait(Duration.ofMinutes(5));


        if (result.getTxStatus() != TxStatus.CONFIRMED)
            throw new IllegalStateException("Not confirmed (" + result.getTxStatus() + "): " + result.getResponse());
        System.out.println("Tx hash   : " + result.getTxHash());


        // 4. Find the token in the minter's wallet
        String unit = AssetUtil.getUnit(policy.getPolicyId(), nftAsset);
        List<Utxo> holding = List.of();
        for (int attempt = 0; attempt < 12 && holding.isEmpty(); attempt++) {
            Thread.sleep(5_000);
            holding = backend.getUtxoService().getUtxos(minter.baseAddress(), unit, 1, 1).getValue();
        }
        if (holding.isEmpty()) throw new IllegalStateException("Token not found yet: " + unit);


        BigInteger quantity = holding.get(0).getAmount().stream()
                .filter(amount -> unit.equals(amount.getUnit()))
                .map(Amount::getQuantity)
                .findFirst().orElseThrow();
        System.out.println("Policy id : " + policy.getPolicyId());
        System.out.println("Quantity  : " + quantity);
    }
}

Running it on Preview prints something like this, with your own values:

Tx hash   : c7050d3519d6d1514c75531e9aa0eb0697d5918882de03d57636245c0b5c1693
Policy id : 787db0464ad195b5c5d0586c3fabfad3d144f6c68e66d1238cf0fef6
Quantity  : 1

To see the metadata, look up your transaction hash in a Preview explorer.

Next steps

Section titled “Next steps”