Solana programs Part 3: understanding Metaplex Token Metadata
May 23, 2022

The metaplex-token-metadata program is the backbone of NFT on Solana.

Imagine you’d like to create an NFT for your art, essentially you need to:

  1. upload your art (digitized) to a permanent storage
  2. create a token mint (i.e., a unique identifier) for your art on Solana
  3. mint one token owned by your wallet

In Step 2, the token mint is special — its supply is only one and it must be associated with information of your art (e.g., name, creator, where it is, etc).

Metaplex has created a specification for such “metadata”, which can be added to every (special) token mint by the token-metadata program.

In this article, we elaborate on the implementation details of token-metadata.

An NFT created on Metaplex

How to Mint NFT with Token Metadata?

The token-metadata program has a good number of instructions (more than 20 in total). The following four are the most commonly used:

  • MetadataInstruction::CreateMetadataAccountV2
  • MetadataInstruction::CreateMasterEditionV3
  • MetadataInstruction::MintNewEditionFromMasterEditionViaToken
  • MetadataInstruction::UpdateMetadataAccountV2
A transaction log on the token-metadata program

1. CreateMetadataAccountV2

First, create a metadata account by calling function process_create_metadata_accounts_v2 :

Note: Every metadata account is a PDA with the token mint (mint_info) as a part of the seeds:

The mint authority (mint_authority_info ) must be a signer.

The Metadata struct has ten fields:

The function basically initializes each field, e.g.,, metadata.update_authority and :

The records the NFT’s attributes (e.g., name, uri and creators):

This metadata account will serve as the master_metadata of the NFT.

2. CreateMasterEditionV3

Then, create a master edition account of the NFT, so that you can use it to print multiple editions (e.g., a limited supply of 10) of your NFT later.

The function process_create_master_edition is used to create a master edition account (edition_account_info ) for a token mint given a max_supply :

Note1: Every master edition account is a PDA with the token mint (mint_info) as a part of the seeds:

Note2: The function can only be called once for a token mint by the update_authority of the token metadata, and only if the supply on the mint is one:

The MasterEdition record has three fields:

pub struct MasterEditionV2 {
pub key: Key,
pub supply: u64,
pub max_supply: Option,}

The function basically initializes these fields:

Finally, it transfers the authority of the token mint (AuthorityType::MintTokensand AuthorityType::FreezeAccount ) to the master edition account:

After that, other token mints may become editions of this metadata, representing limited editions of the NFT.

3. MintNewEditionFromMasterEditionViaToken

The function process_mint_new_edition_from_master_edition_via_token is used to mint new editions of an NFT from its master edition:

The caller provides a new mint account and an edition number, and must be signer of the’s token account (i.e., an owner of the NFT):

The function will create a new edition_marker PDA using the edition number and the NFT’s mint ( as a part of the seeds:

Then, the function mint_limited_edition is called to mint the new edition:

In mint_limited_edition , a new metadata account will be created based on the new mint account (mint_info):

The new mint must be different from and its supply must be one:

The new mint account is also part of the seeds for creating the new edition PDA:

Finally, similar to that in CreateMasterEditionV3 , the new mint account’s authority (AuthorityType::MintTokens and AuthorityType::FreezeAccount ) is set to the new edition account:

4. UpdateMetadataAccountV2

The function process_update_metadata_accounts_v2 can be used to update the metadata at any time by the metadata’s update_authority:

To update the record, metadata.is_mutable must be true :

The metadata’s update_authority can also be updated, as well as metadata.primary_sale_happened :

Other Token Metadata instructions

The token-metadata program has several other functionalities such as verifying the NFT creators (see full code):

MetadataInstruction::SignMetadata => {
    msg!(“Instruction: Sign Metadata”);
    process_sign_metadata(program_id, accounts)}
MetadataInstruction::RemoveCreatorVerification => {
    msg!("Instruction: Remove Creator Verification");
    process_remove_creator_verification(program_id, accounts)}

In the next few articles, we will continue to highlight the technical details of a few more popular Solana programs.

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