Creating Compressed NFTs with JavaScript

Compressed NFTs on Solana use the Bubblegum program from Metaplex to cheaply and securely store NFT metadata using State Compression.

This developer guide will use JavaScript/TypeScript to demonstrate:

• how to create a tree for compressed NFTs,
• how to mint compressed NFTs into a tree,
• how to get compressed NFT metadata from the Read API, and
• how to transfer compressed NFTs

Intro to Compressed NFTs #

Compressed NFTs use State Compression and merkle trees to drastically reduce the storage cost for NFTs. Instead of storing an NFT's metadata in a typical Solana account, compressed NFTs store the metadata within the ledger. This allows compressed NFTs to still inherit the security and speed of the Solana blockchain, while at the same time reducing the overall storage costs.

Even though the on-chain data storage mechanism is different than their uncompressed counterparts, compressed NFTs still follow the exact same Metadata schema/structure. Allowing you to define your Collection and NFT in an identical way.

However, the process to mint and transfer compressed NFTs is different from uncompressed NFTs. Aside from using a different on-chain program, compressed NFTs are minting into a merkle tree and require verification of a "proof" to transfer. More on this below.

Compressed NFTs and indexers #

Since compressed NFTs store all of their metadata in the ledger, instead of in traditional accounts like uncompressed NFTs, we will need to help of indexing services to quickly fetch our compressed NFT's metadata.

Supporting RPC providers are using the Digital Asset Standard Read API (or "Read API" for short) to add additional RPC methods that developers can call. These additional, NFT oriented methods, are loaded with all the information about particular NFTs. Including support for BOTH compressed NFTs AND uncompressed NFTs.

Metadata is secured by the ledger and cached by indexers #

Since validators do not keep a very long history of the recent ledger data, these indexers effectively "cache" the compressed NFT metadata passed through the Solana ledger. Quickly serving it back on request to improve speed and user experience of applications. However, since the metadata was already secured by the ledger when minting the compressed NFT, anyone could re-index the metadata directly from the secure ledger. Allowing for independent verification of the data, should the need or desire arise.

These indexing services are already available from some of the common RPC providers, with more rolling out support in the near future. To name a few of the RPC providers that already support the Read API:

• Helius
• Triton
• SimpleHash

How to mint compressed NFTs #

The process to create or mint compressed NFTs on Solana is similar to creating a "traditional NFT collection", with a few differences. The mint process will happen in 3 primary steps:

• create an NFT collection (or use an existing one)
• create a concurrent merkle tree (using the @solana/spl-account-compression SDK)
• mint compressed NFTs into your tree (to any owner's address you want)

How to transfer a compressed NFT #

Once your compressed NFT exists on the Solana blockchain, the process to transfer ownership of a compressed NFT happens in a few broad steps:

1. get the NFT "asset" information (from the indexer)
2. get the NFT's "proof" (from the indexer)
3. get the Merkle tree account (from the Solana blockchain)
4. prepare the asset proof (by parsing and formatting it)
5. build and send the transfer instruction

The first three steps primarily involve gathering specific pieces of information (the proof and the tree's canopy depth) for the NFT to be transferred. These pieces of information are needed to correctly parse/format the proof to actually be sent within the transfer instruction itself.

Getting started #

For this guide, we are going to make a few assumptions about the compressed NFT collection we are going to create:

• we are going to use TypeScript and NodeJS for this example
• we will use a single, new Metaplex collection

Project Setup #

Before we start creating our compressed NFT collection, we need to install a few packages:

• @solana/web3.js - the base Solana JS SDK for interacting with the blockchain, including making our RPC connection and sending transactions
• @solana/spl-token - used in creating our collection and mint on-chain
• @solana/spl-account-compression - used to create the on-chain tree to store our compressed NFTs
• @metaplex-foundation/mpl-bubblegum - used to get the types and helper functions for minting and transferring compressed NFTs on-chain
• @metaplex-foundation/mpl-token-metadata - used to get the types and helper functions for our NFT's metadata

Using your preferred package manager (e.g. npm, yarn, pnpm, etc), install these packages into your project:

yarn add @solana/web3.js @solana/spl-token @solana/spl-account-compression

yarn add @metaplex-foundation/mpl-bubblegum @metaplex-foundation/mpl-token-metadata

Create a Collection #

NFTs are normally grouped together into a Collection using the Metaplex standard. This is true for BOTH traditional NFTs AND compressed NFTs. The NFT Collection will store all the broad metadata for our NFT grouping, such as the collection image and name that will appear in wallets and explorers.

Under the hood, an NFT collection acts similar to any other token on Solana. More specifically, a Collection is effectively a uncompressed NFT. So we actually create them following the same process of creating an SPL token:

• create a new token "mint"
• create a associated token account (ata) for our token mint
• actually mint a single single token
• store the collection's metadata in an Account on-chain

Since NFT Collections having nothing special to do with State Compression or compressed NFTs, we will not cover creating one in this guide.

Collection addresses #

Even though this guide does not cover creating one, we will need the many of the various addresses for your Collection, including:

• collectionAuthority - this may be your payer but it also might not be
• collectionMint - the collection's mint address
• collectionMetadata - the collection's metadata account
• editionAccount - for example, the masterEditionAccount created for your collection

Create a tree #

One of the most important decisions to make when creating compressed NFTs is how to setup your tree. Especially since the values used to size your tree will determine the overall cost of creation, and CANNOT be changed after creation.

Tree vs Collection #

A tree is NOT the same thing as a collection. A single collection can use any number of trees. In fact, this is usually recommended for larger collections due to smaller trees having greater composability.

Conversely, even though a tree could be used in multiple collections, it is generally considered an anti-pattern and is not recommended.

Using the helper functions provided by the @solana/spl-account-compression SDK, we can create our tree in the following steps:

• decide on our tree size
• generate a new Keypair and allocated space for the tree on-chain
• actually create the tree (making it owned by the Bubblegum program)

Size your tree #

Your tree size is set by 3 values, each serving a very specific purpose:

1. maxDepth - used to determine how many NFTs we can have in the tree
2. maxBufferSize - used to determine how many updates to your tree are possible in the same block
3. canopyDepth - used to store a portion of the proof onchain, and as such is a large of cost and composability of your compressed NFT collection

Let's assume we are going to create a compressed NFT collection with 10k NFTs in it. And since our collection is relatively small, we only need a single smaller tree to store all the NFTs:

// define the depth and buffer size of our tree to be created
const maxDepthSizePair: ValidDepthSizePair = {
  // max=16,384 nodes (for a `maxDepth` of 14)
  maxDepth: 14,
  maxBufferSize: 64,
};
 
// define the canopy depth of our tree to be created
const canopyDepth = 10;

Setting a maxDepth of 14 will allow our tree to hold up to 16,384 compressed NFTs, more than exceeding our 10k collection size.

Since only specific ValidDepthSizePair pairs are allowed, simply set the maxBufferSize to the corresponding value tied to your desired maxDepth.

Next, setting canopyDepth of 10 tells our tree to store 10 of our "proof node hashes" on-chain. Thus requiring us to always include 4 proof node values (i.e. maxDepth - canopyDepth) in every compressed NFT transfer instruction.

Generate addresses for the tree #

When creating a new tree, we need to generate a new Keypair address for the tree to have:

const treeKeypair = Keypair.generate();

Since our tree will be used for compressed NFTs, we will also need to derive an Account with authority that is owned by the Bubblegum program (i.e. PDA):

// derive the tree's authority (PDA), owned by Bubblegum
const [treeAuthority, _bump] = PublicKey.findProgramAddressSync(
  [treeKeypair.publicKey.toBuffer()],
  BUBBLEGUM_PROGRAM_ID,
);

Build the tree creation instructions #

With our tree size values defined, and our addresses generated, we need to build two related instructions:

1. allocate enough space on-chain for our tree
2. actually create the tree, owned by the Bubblegum program

Using the createAllocTreeIx helper function, we allocate enough space on-chain for our tree.

// allocate the tree's account onchain with the `space`
const allocTreeIx = await createAllocTreeIx(
  connection,
  treeKeypair.publicKey,
  payer.publicKey,
  maxDepthSizePair,
  canopyDepth,
);

Then using the createCreateTreeInstruction from the Bubblegum SDK, we actually create the tree on-chain. Making it owned by the Bubblegum program.

// create the instruction to actually create the tree
const createTreeIx = createCreateTreeInstruction(
  {
    payer: payer.publicKey,
    treeCreator: payer.publicKey,
    treeAuthority,
    merkleTree: treeKeypair.publicKey,
    compressionProgram: SPL_ACCOUNT_COMPRESSION_PROGRAM_ID,
    // NOTE: this is used for some onchain logging
    logWrapper: SPL_NOOP_PROGRAM_ID,
  },
  {
    maxBufferSize: maxDepthSizePair.maxBufferSize,
    maxDepth: maxDepthSizePair.maxDepth,
    public: false,
  },
  BUBBLEGUM_PROGRAM_ID,
);

Build and send the transaction #

With our two instructions built, we can add them into a transaction and send them to the blockchain, making sure both the payer and generated treeKeypair sign the transaction:

// build the transaction
const tx = new Transaction().add(allocTreeIx).add(createTreeIx);
tx.feePayer = payer.publicKey;
 
// send the transaction
const txSignature = await sendAndConfirmTransaction(
  connection,
  tx,
  // ensuring the `treeKeypair` PDA and the `payer` are BOTH signers
  [treeKeypair, payer],
  {
    commitment: "confirmed",
    skipPreflight: true,
  },
);

After a few short moments, and once the transaction is confirmed, we are ready to start minting compressed NFTs into our tree.

Mint compressed NFTs #

Since compressed NFTs follow the same Metaplex metadata standards as traditional NFTs, we can define our actual NFTs data the same way.

The primary difference is that with compressed NFTs the metadata is actually stored in the ledger (unlike traditional NFTs that store them in accounts). The metadata gets "hashed" and stored in our tree, and by association, secured by the Solana ledger.

Allowing us to cryptographically verify that our original metadata has not changed (unless we want it to).

Define our NFT's metadata #

We can define the specific metadata for the single NFT we are about to mint:

const compressedNFTMetadata: MetadataArgs = {
  name: "NFT Name",
  symbol: "ANY",
  // specific json metadata for each NFT
  uri: "https://supersweetcollection.notarealurl/token.json",
  creators: null,
  editionNonce: 0,
  uses: null,
  collection: null,
  primarySaleHappened: false,
  sellerFeeBasisPoints: 0,
  isMutable: false,
  // these values are taken from the Bubblegum package
  tokenProgramVersion: TokenProgramVersion.Original,
  tokenStandard: TokenStandard.NonFungible,
};

In this demo, the key pieces of our NFT's metadata to note are:

• name - this is the actual name of our NFT that will be displayed in wallets and on explorers.
• uri - this is the address for your NFTs metadata JSON file.
• creators - for this example, we are not storing a list of creators. If you want your NFTs to have royalties, you will need to store actual data here. You can checkout the Metaplex docs for more info on it.

Derive the Bubblegum signer #

When minting new compressed NFTs, the Bubblegum program needs a PDA to perform a cross-program invocation (cpi) to the SPL compression program.

Below, we derive this PDA using the required hard coded seed string of collection_cpi:

// derive a PDA (owned by Bubblegum) to act as the signer of the compressed minting
const [bubblegumSigner, _bump2] = PublicKey.findProgramAddressSync(
  // `collection_cpi` is a custom prefix required by the Bubblegum program
  [Buffer.from("collection_cpi", "utf8")],
  BUBBLEGUM_PROGRAM_ID,
);

Create the mint instruction #

Now we should have all the information we need to actually mint our compressed NFT.

Using the createMintToCollectionV1Instruction helper function provided in the Bubblegum SDK, we can craft the instruction to actually mint our compressed NFT directly into our collection.

If you have minted traditional NFTs on Solana, this will look fairly similar. We are creating a new instruction, giving several of the account addresses you might expect (e.g. the payer, tokenMetadataProgram, and various collection addresses), and then some tree specific addresses.

The addresses to pay special attention to are:

• leafOwner - this will be the owner of the compressed NFT. You can either mint it your self (i.e. the payer), or airdrop to any other Solana address
• leafDelegate - this is the delegated authority of this specific NFT we are about to mint. If you do not want to have a delegated authority for the NFT we are about to mint, then this value should be set to the same address of leafOwner.

const compressedMintIx = createMintToCollectionV1Instruction(
  {
    payer: payer.publicKey,
 
    merkleTree: treeAddress,
    treeAuthority,
    treeDelegate: payer.publicKey,
 
    // set the receiver of the NFT
    leafOwner: receiverAddress || payer.publicKey,
    // set a delegated authority over this NFT
    leafDelegate: payer.publicKey,
 
    // collection details
    collectionAuthority: payer.publicKey,
    collectionAuthorityRecordPda: BUBBLEGUM_PROGRAM_ID,
    collectionMint: collectionMint,
    collectionMetadata: collectionMetadata,
    editionAccount: collectionMasterEditionAccount,
 
    // other accounts
    bubblegumSigner: bubblegumSigner,
    compressionProgram: SPL_ACCOUNT_COMPRESSION_PROGRAM_ID,
    logWrapper: SPL_NOOP_PROGRAM_ID,
    tokenMetadataProgram: TOKEN_METADATA_PROGRAM_ID,
  },
  {
    metadataArgs: Object.assign(compressedNFTMetadata, {
      collection: { key: collectionMint, verified: false },
    }),
  },
);

Some of the other tree specific addresses are:

• merkleTree - the address of our tree we created
• treeAuthority - the authority of the tree
• treeDelegate - the delegated authority of the entire tree

Then we also have all of our NFT collection's addresses, including the mint address, metadata account, and edition account. These addresses are also standard to pass in when minting uncompressed NFTs.

Sign and send the transaction #

Once our compressed mint instruction has been created, we can add it to a transaction and send it to the Solana network:

const tx = new Transaction().add(compressedMintIx);
tx.feePayer = payer.publicKey;
 
// send the transaction to the cluster
const txSignature = await sendAndConfirmTransaction(connection, tx, [payer], {
  commitment: "confirmed",
  skipPreflight: true,
});

Reading compressed NFTs metadata #

With the help of a supporting RPC provider, developers can use the Digital Asset Standard Read API (or "Read API" for short) to fetch the metadata of NFTs.

Using the Read API #

When working with the Read API and a supporting RPC provider, developers can make POST requests to the RPC endpoint using your preferred method of making such requests (e.g. curl, JavaScript fetch(), etc).

A note about the Asset ID #

Within the Read API, digital assets (i.e. NFTs) are indexed by their id. This asset id value differs slightly between traditional NFTs and compressed NFTs:

• for traditional/uncompressed NFTs: this is the token's address for the actual Account on-chain that stores the metadata for the asset.
• for compressed NFTs: this is the id of the compressed NFT within the tree and is NOT an actual on-chain Account address. While a compressed NFT's assetId resembles a traditional Solana Account address, it is not.

Common Read API Methods #

While the Read API supports more than these listed below, the most commonly used methods are:

• getAsset - get a specific NFT asset by its id
• getAssetProof - returns the merkle proof that is required to transfer a compressed NFT, by its asset id
• getAssetsByOwner - get the assets owned by a specific address
• getAssetsByGroup - get the assets by a specific grouping (i.e. a collection)

Read API Methods, Schema, and Specification #

Explore all the additional RPC methods added by Digital Asset Standard Read API on Metaplex's RPC Playground. Here you will also find the expected inputs and response schema for each supported RPC method.

Example Read API Request #

For demonstration, below is an example request for the getAsset method using the JavaScript Fetch API, which is built into modern JavaScript runtimes:

// make a POST request to the RPC using the JavaScript `fetch` api
const response = await fetch(rpcEndpointUrl, {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    jsonrpc: "2.0",
    id: "rpd-op-123",
    method: "getAsset",
    params: {
      id: "5q7qQ4FWYyj4vnFrivRBe6beo6p88X8HTkkyVPjPkQmF",
    },
  }),
});

Example Read API Response #

With a successful response from the RPC, you should seem similar data to this:

{
  interface: 'V1_NFT',
  id: '5q7qQ4FWYyj4vnFrivRBe6beo6p88X8HTkkyVPjPkQmF',
  content: [Object],
  authorities: [Array],
  compression: [Object],
  grouping: [],
  royalty: [Object],
  creators: [],
  ownership: [Object],
  supply: [Object],
  mutable: false
}

The response fields to pay special attention to are:

• id - this is your asset's id
• grouping - can tell you the collection address that the NFT belongs to. The collection address will be the group_value.
• metadata - contains the actual metadata for the NFT, including the auto fetched JSON uri set when the NFT was minted
• ownership - gives you the NFT owner's address (and also if the NFT has delegated authority to another address)
• compression - tells you if this NFT is actually using compression or not. For compressed NFTs, this will also give you the tree address that is storing the compressed NFT onchain.

Transfer compressed NFTs #

Transferring compressed NFTs is different from transferring uncompressed NFTs. Aside from using a different on-chain program, compressed NFTs require the use of an asset's "merkle proof" (or proof for short) to actually change ownership.

What is a merkle proof? #

An asset's "merkle proof" is a listing of all the "adjacent hashes" within the tree that are required to validate a specific leaf within said tree.

These proof hashes themselves, and the specific asset's leaf data, are hashed together in a deterministic way to compute the "root hash". Therefore, allowing for cryptographic validation of an asset within the merkle tree.

Transferring ownership of a compressed NFT happens in 5 broad steps:

1. get the NFT's "asset" data (from the indexer)
2. get the NFT's proof (from the indexer)
3. get the Merkle tree account (directly from the Solana blockchain)
4. prepare the asset proof
5. build and send the transfer instruction

The first three steps primarily involve gathering specific pieces of information (the proof and the tree's canopy depth) for the NFT to be transferred. These pieces of information are needed to correctly parse/format the proof to actually be sent within the transfer instruction itself.

Get the asset #

To perform the transfer of our compressed NFT, we will need to retrieve a few pieces of information about the NFT.

For starters, we will need to get some the asset's information in order to allow the on-chain compression program to correctly perform validation and security checks.

We can use the getAsset RPC method to retrieve two important pieces of information for the compressed NFT: the data_hash and creator_hash.

Example response from the getAsset method #

Below is an example response from the getAsset method:

compression: {
  eligible: false,
  compressed: true,
  data_hash: 'D57LAefACeaJesajt6VPAxY4QFXhHjPyZbjq9efrt3jP',
  creator_hash: '6Q7xtKPmmLihpHGVBA6u1ENE351YKoyqd3ssHACfmXbn',
  asset_hash: 'F3oDH1mJ47Z7tNBHvrpN5UFf4VAeQSwTtxZeJmn7q3Fh',
  tree: 'BBUkS4LZQ7mU8iZXYLVGNUjSxCYnB3x44UuPVHVXS9Fo',
  seq: 3,
  leaf_id: 0
}

Get the asset proof #

The next step in preparing your compressed NFT transfer instruction, is to get a valid asset proof to perform the transfer. This proof is required by the on-chain compression program to validate on-chain information.

We can use the getAssetProof RPC method to retrieve two important pieces of information:

• proof - the "full proof" that is required to perform the transfer (more on this below)
• tree_id - the on-chain address of the compressed NFTs tree

Full proof is returned #

The getAssetProof RPC method returns the complete listing of "proof hashes" that are used to perform the compressed NFT transfer. Since this "full proof" is returned from the RPC, we will need to remove the portion of the "full proof" that is stored on-chain via the tree's canopy.

Example response from the getAssetProof method #

Below is an example response from the getAssetProof method:

{
  root: '7dy5bzgaRcUnNH2KMExwNXXNaCJnf7wQqxc2VrGXy9qr',
  proof: [
    'HdvzZ4hrPEdEarJfEzAavNJEZcCS1YU1fg2uBvQGwAAb',
    ...
    '3e2oBSLfSDVdUdS7jRGFKa8nreJUA9sFPEELrHaQyd4J'
  ],
  node_index: 131072,
  leaf: 'F3oDH1mJ47Z7tNBHvrpN5UFf4VAeQSwTtxZeJmn7q3Fh',
  tree_id: 'BBUkS4LZQ7mU8iZXYLVGNUjSxCYnB3x44UuPVHVXS9Fo'
}

Get the Merkle tree account #

Since the getAssetProof will always return the "full proof", we will have to reduce it down in order to remove the proof hashes that are stored on-chain in the tree's canopy. But in order to remove the correct number of proof addresses, we need to know the tree's canopyDepth.

Once we have our compressed NFT's tree address (the tree_id value from getAssetProof), we can use the ConcurrentMerkleTreeAccount class, from the @solana/spl-account-compression SDK:

// retrieve the merkle tree's account from the blockchain
const treeAccount = await ConcurrentMerkleTreeAccount.fromAccountAddress(
  connection,
  treeAddress,
);
 
// extract the needed values for our transfer instruction
const treeAuthority = treeAccount.getAuthority();
const canopyDepth = treeAccount.getCanopyDepth();

For the transfer instruction, we will also need the current treeAuthority address which we can also get via the treeAccount.

Prepare the asset proof #

With our "full proof" and canopyDepth values on hand, we can correctly format the proof to be submitted within the transfer instruction itself.

Since we will use the createTransferInstruction helper function from the Bubblegum SDK to actually build our transfer instruction, we need to:

• remove the proof values that are already stored on-chain in the tree's canopy, and
• convert the remaining proof values into the valid AccountMeta structure that the instruction builder function accepts

// parse the list of proof addresses into a valid AccountMeta[]
const proof: AccountMeta[] = assetProof.proof
  .slice(0, assetProof.proof.length - (!!canopyDepth ? canopyDepth : 0))
  .map((node: string) => ({
    pubkey: new PublicKey(node),
    isSigner: false,
    isWritable: false,
  }));

In the TypeScript code example above, we are first taking a slice of our "full proof", starting at the beginning of the array, and ensuring we only have proof.length - canopyDepth number of proof values. This will remove the portion of the proof that is already stored on-chain in the tree's canopy.

Then we are structuring each of the remaining proof values as a valid AccountMeta, since the proof is submitted on-chain in the form of "extra accounts" within the transfer instruction.

Build the transfer instruction #

Finally, with all the required pieces of data about our tree and compressed NFTs, and a correctly formatted proof, we are ready to actually create the transfer instruction.

Build your transfer instruction using the createTransferInstruction helper function from the Bubblegum SDK:

// create the NFT transfer instruction (via the Bubblegum package)
const transferIx = createTransferInstruction(
  {
    merkleTree: treeAddress,
    treeAuthority,
    leafOwner,
    leafDelegate,
    newLeafOwner,
    logWrapper: SPL_NOOP_PROGRAM_ID,
    compressionProgram: SPL_ACCOUNT_COMPRESSION_PROGRAM_ID,
    anchorRemainingAccounts: proof,
  },
  {
    root: [...new PublicKey(assetProof.root.trim()).toBytes()],
    dataHash: [...new PublicKey(asset.compression.data_hash.trim()).toBytes()],
    creatorHash: [
      ...new PublicKey(asset.compression.creator_hash.trim()).toBytes(),
    ],
    nonce: asset.compression.leaf_id,
    index: asset.compression.leaf_id,
  },
  BUBBLEGUM_PROGRAM_ID,
);

Aside from passing in our assorted Account addresses and the asset's proof, we are converting the string values of our data_hash, creator_hash, root hash into an array of bytes that is accepted by the createTransferInstruction helper function.

Since each of these hash values resemble and are formatted similar to PublicKeys, we can use the PublicKey class in web3.js to convert them into an accepted byte array format.

Send the transaction #

With our transfer instructions built, we can add it into a transaction and send it to the blockchain similar to before. Making sure either the current leafOwner or the leafDelegate signs the transaction.

And once confirmed by the cluster, we will have successfully transferred a compressed NFT.

Example code repository #

You can find an example code repository for this developer guide on the Solana Developers GitHub: https://github.com/solana-developers/compressed-nfts