> ## Documentation Index
> Fetch the complete documentation index at: https://developers.circle.com/llms.txt
> Use this file to discover all available pages before exploring further.

# NFT template

The NFT template is an audited, ready-to-deploy smart contract for creating and
managing NFTs. It implements the ERC-721 standard, which is widely used for
representing non-fungible tokens (NFTs) on a blockchain. Unlike ERC-20 tokens,
which represent fungible and interchangeable assets, ERC-721 NFTs are unique and
non-interchangeable, making them suitable for digital collectibles, gaming
assets, and many other use cases.

The ERC-721 NFT standard has gained significant popularity and has been
implemented by numerous projects and platforms. Some key use cases for ERC-721
NFTs include:

* **Digital collectibles:** ERC-721 NFTs are extensively used for creating and
  trading unique digital collectibles. These collectibles can represent various
  items such as artwork, trading cards, virtual pets, in-game assets, and more.

* **Tokenized assets:** ERC-721 NFTs can represent ownership in real-world
  assets such as real estate, artwork, jewelry, and other physical assets. This
  enables fractional ownership, providing liquidity and opening up investment
  opportunities.

* **Gaming assets:** ERC-721 NFTs are a perfect fit for representing in-game
  assets, enabling players to own, trade, and transfer virtual items securely
  and transparently. This functionality has facilitated the emergence of
  blockchain-based gaming ecosystems.

In this comprehensive guide, you explore the NFT template, which provides all
the necessary information to deploy and understand the contract's common
functions.

## Deployment parameters

The NFT template creates a customized, fully compliant ERC-721 smart contract.
To create a contract using this template, provide the following parameter values
when deploying a smart contract template using the
[`POST: /templates/{id}/deploy`](/api-reference/contracts/smart-contract-platform/deploy-contract-template)
API.

**Template ID:** 76b83278-50e2-4006-8b63-5b1a2a814533

### Template deployment parameters

|        Parameter       | Type      | Required |                                                                                                  Description                                                                                                 |
| :--------------------: | --------- | :------: | :----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------: |
|         `name`         | String    |     X    |                                                                    Name of the contract - stored as a property of the contract on-chain.                                                                     |
|        `symbol`        | String    |          |                                                           Symbol of the token - stored onchain. The symbol is usually 3 or 4 characters in length.                                                           |
|     `defaultAdmin`     | String    |     X    |     The address of the default admin. This address can execute permissioned functions on the contract. You will lose administrative access to the contract if this is not set to an address you control.     |
| `primarySaleRecipient` | String    |     X    |                                                                                 The recipient address for first-time sales.                                                                                  |
| `platformFeeRecipient` | String    |          |                                      The recipient address for all sale fees. You can set this to your address if you are deploying a template on someone else's behalf.                                     |
|  `platformFeePercent`  | Float     |          |                           The percentage of sales that go to the platform fee recipient. For example, set it as 0.1 if you want 10% of sales fees to go to *platformFeeRecipient*.                           |
|   `royaltyRecipient`   | String    |     X    |                               The recipient address for all royalties (secondary sales). This allows the contract creator to benefit from further sales of the contract token.                               |
|    `royaltyPercent`    | Float     |     X    |                           The percentage of secondary sales that go to the royalty recipient. For example, set it as 0.05 if you want royalties to be 5% of secondary sales value.                           |
|      `contractUri`     | String    |          | The URL for the marketplace metadata of your contract. This is used on marketplaces like OpenSea. See [Contract-level Metadata](https://docs.opensea.io/docs/contract-level-metadata) for more information.  |
|   `trustedForwarders`  | String\[] |          |                      A list of addresses that can forward ERC2771 meta-transactions to this contract. See [ethereum.org](https://eips.ethereum.org/EIPS/eip-2771) for more information.                      |

Here is an example of the `templateParameters` JSON object within the request
body to
[deploy a contract from a template](/api-reference/contracts/smart-contract-platform/deploy-contract-template)
for the ERC-721 NFT template.

<Note>
  In this example, the `defaultAdmin`, `primarySaleRecipient`, and
  `royaltyRecipient` parameters are the same address but can be set distinctly
  based on your use case.
</Note>

```json JSON theme={null}
...
"templateParameters": {
  "name": "My NFT Contract",
  "defaultAdmin": "0x4F77E56dfA40990349e1078e97AC3Eb479e0dAc6",
  "primarySaleRecipient": "0x4F77E56dfA40990349e1078e97AC3Eb479e0dAc6",
  "royaltyRecipient": "0x4F77E56dfA40990349e1078e97AC3Eb479e0dAc6",
  "royaltyPercent": 0.05
}
```

## Common functions

This section lists the most commonly used functions on NFT template, their
respective parameters and potential failure scenarios. These functions include:

* [approve \[write\]](#approve-write)

* [mintTo \[write\]](#mintto-write)

* [safeTransferFrom \[write\]](#safetransferfrom-write)

* [setTokenURI \[write\]](#settokenuri-write)

* [ownerOf \[read\]](#ownerof-read)

* [balanceOf \[read\]](#balanceof-address-owner-read)

<Note>
  At this time, not all failure scenarios or error messages received from the
  blockchain are passed through Circle's APIs. Instead, you will receive a
  generic [`ESTIMATION_ERROR`](/contracts/error-codes#transaction-errors) error.
  If available, the `errorDetails` field will have more information on the cause
  of failure.
</Note>

## approve \[write]

The approve function allows the owner of an ERC721 NFT to approve another
address to transfer the token on their behalf.

### Parameters

| Parameter | Type    | Description                                              |
| :-------- | :------ | :------------------------------------------------------- |
| `to`      | address | The address approved to transfer the token.              |
| `tokenId` | unit256 | The identifier of the token being approved for transfer. |

**Failure Scenarios:**

* If the *to* address matches the current owner of the token (owner), the
  function will fail. This check ensures that the approval is not granted to the
  same owner, preventing unnecessary approvals. *"ERC721: approval to current
  owner"*
* The function requires that the caller `_msgSender` either be the token's owner
  or have been approved for all by the owner. If this condition is not met, the
  function will fail. This validation prevents unauthorized users from approving
  transfers on behalf of the token owner. *"ERC721: approve caller is not token
  owner or approved for all"*

```solidity Solidity theme={null}
function approve(address to, uint256 tokenId) public virtual override {
  address owner = ERC721Upgradeable.ownerOf(tokenId);
  require(to != owner, "ERC721: approval to current owner");

  require(
    _msgSender() == owner || isApprovedForAll(owner, _msgSender()),
    "ERC721: approve caller is not token owner or approved for all"
  );

  _approve(to, tokenId);
}
```

## mintTo \[write]

The `mintTo` function is a function that mints a new NFT and assigns it to a
specific address. This function can only be called by an address with the
`MINTER_ROLE`.

### Parameters

| Parameter | Type    | Description                                                    |
| :-------- | :------ | :------------------------------------------------------------- |
| `to`      | address | The address to which the minted NFT will be assigned.          |
| `uri`     | string  | The URI (Uniform Resource Identifier) of the newly minted NFT. |

### Returns

| Parameter       |         |                                          |
| :-------------- | :------ | :--------------------------------------- |
| `tokenIdToMint` | uint256 | The unique identifier of the minted NFT. |

### Failure scenarios

* If the caller of the function does not have the `MINTER_ROLE` assigned, the
  function will fail and throw an exception. *"AccessControl: account ",
  StringsUpgradeable.toHexString(account), " is missing role ",
  StringsUpgradeable.toHexString(uint256(role), 32)*
* The function checks if the length of the \_uri string is greater than 0,
  ensuring that the URI is not empty.\
  *"empty uri."*
* *The function checks that the to address is not the zero address.*\
  *"ERC721: mint to the zero address"*
* The function checks that the `tokenId` has not already been created. *"ERC721:
  token already minted"*

```solidity Solidity theme={null}
function mintTo(address _to, string calldata _uri) external onlyRole(MINTER_ROLE) returns (uint256) {
  // `_mintTo` is re-used. `mintTo` just adds a minter role check.
  return _mintTo(_to, _uri);
}

function _mintTo(address _to, string calldata _uri) internal returns (uint256 tokenIdToMint) {
  tokenIdToMint = nextTokenIdToMint;
  nextTokenIdToMint += 1;

  require(bytes(_uri).length > 0, "empty uri.");
  _setTokenURI(tokenIdToMint, _uri);

  _safeMint(_to, tokenIdToMint);

  emit TokensMinted(_to, tokenIdToMint, _uri);
}
```

## safeTransferFrom \[write]

This function allows the transfer of an ERC721 NFT from the `from` address to
the `to` address. It requires that the caller is the token owner or has been
approved to transfer the token.

### Parameters

| Parameter | Type    | Description                                               |
| :-------- | :------ | :-------------------------------------------------------- |
| `from`    | address | The address that owns the token and wants to transfer it. |
| `to`      | address | The address that will receive ownership of the token.     |
| `tokenId` | unit256 | The unique identifier of the token being transferred.     |

### Failure scenarios

* The `isApprovedOrOwner` function is called to check if the caller is the token
  owner or an approved address. This check ensures that the transfer can only be
  performed by the token owner or an approved address.\
  *"ERC721: caller is not token owner or approved"*
* If the to address is a contract, the `checkOnERC721Received` function is
  called to check if the to address is a contract that implements the
  `onERC721Received` function correctly - according to the ERC721 standard.
* It checks if the token being transferred `tokenId` parameter is owned by the
  `from` address parameter. *"ERC721: transfer from incorrect owner"*
* It checks that the `to` address parameter is not the zero address. If it is
  the zero address, the function throws an exception with the message.\
  *"ERC721: transfer to the zero address"*
* If the transfer is restricted on the contract, it still allows burning and
  minting. It checks whether the `TRANSFER_ROLE` is assigned to either the
  `from` or `to` address. This ensures that token transfers comply with specific
  access control restrictions defined by the contract.\
  *"restricted to TRANSFER\_ROLE holders”*
* The function will check if the `to` address is a contract. If it is, the
  `_checkOnERC721Received` hook will check if the receiver address properly
  handles the received token. I\
  *"ERC721: transfer to non ERC721Receiver implementer"*

```solidity Solidity theme={null}
// safeTransferFrom
function safeTransferFrom(address from, address to, uint256 tokenId) public virtual override {
  safeTransferFrom(from, to, tokenId, "");
}

// safeTransferFrom - with data parameter
function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory data) public virtual override {
  require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: caller is not token owner or approved");
  _safeTransfer(from, to, tokenId, data);
}
```

## setTokenURI \[write]

This function is responsible for setting the metadata URI for a specific NFT
token.

### Parameters

| Parameter | Type    | Description                                                                     |
| :-------- | :------ | :------------------------------------------------------------------------------ |
| `tokenId` | unit256 | The unique identifier of the NFT token for which the metadata URI is being set. |
| `uri`     | string  | The new metadata URI that will be associated with the NFT token.                |

### Failure scenarios

* The function checks if the caller is authorized to set the metadata URI. It
  calls the `canSetMetadata` function, which checks the authorization based on
  certain conditions specified in the contract.\
  *"NFTMetadata: not authorized to set metadata."*
* The function verifies if the metadata URI is not frozen. It checks the
  `uriFrozen` boolean flag to determine if the metadata is in a frozen state. If
  the metadata is frozen, meaning it cannot be changed, the function will throw
  an exception.\
  *"NFTMetadata: metadata is frozen."*
* If the provided URI is empty, the function will throw an exception with the
  message\
  *"NFTMetadata: empty metadata."*

```solidity Solidity theme={null}
function setTokenURI(uint256 _tokenId, string memory _uri) public virtual {
  require(_canSetMetadata(), "NFTMetadata: not authorized to set metadata.");
  require(!uriFrozen, "NFTMetadata: metadata is frozen.");
  _setTokenURI(_tokenId, _uri);
}

function _setTokenURI(uint256 _tokenId, string memory _uri) internal virtual {
  require(bytes(_uri).length > 0, "NFTMetadata: empty metadata.");
  _tokenURI[_tokenId] = _uri;

  emit MetadataUpdate(_tokenId);
}
```

## ownerOf \[read]

This function is used to retrieve the address of the owner of the ERC721 NFT
with the specified `tokenId`.

### Parameters

| Parameter | Type    | Description                                                                        |
| :-------- | :------ | :--------------------------------------------------------------------------------- |
| `tokenId` | unit256 | The unique identifier of the token for which the owner's address is being fetched. |

### Failure scenarios

* The function checks if the owner's address is not the zero address. This check
  is performed to ensure that a valid owner address is returned. *"ERC721:
  invalid token ID"*

### Note

* The function does not revert if the token doesn't exist. The zero address will
  be returned.

```solidity Solidity theme={null}
function ownerOf(uint256 tokenId) public view virtual override returns (address) {
  address owner = _ownerOf(tokenId);
  require(owner != address(0), "ERC721: invalid token ID");
  return owner;
}
```

## balanceOf \[read]

This function retrieves the balance (number of tokens) owned by a specific owner
address.

### Parameters

| Parameter |         |                                                           |
| :-------- | :------ | :-------------------------------------------------------- |
| `owner`   | address | The address for which the token balance is being fetched. |

### Failure scenarios

* The function checks if the `owner` address is not the zero address. The zero
  address represents an invalid or nonexistent address. *"ERC721: address zero
  is not a valid owner"*

```solidity Solidity theme={null}
function balanceOf(address owner) public view virtual override returns (uint256) {
  require(owner != address(0), "ERC721: address zero is not a valid owner");
  return _balances[owner];
}
```