ERC-721
ERC-721 is the standard for non-fungible tokens (NFTs) on the Ethereum blockchain. Unlike ERC-20 tokens, which are interchangeable, every ERC-721 token is unique and distinct, identified by a specific 'Token ID' within a smart contract. This standard allows developers to track, own, and transfer unique digital items such as artwork, collectibles, or digital identity assets. By providing a uniform interface, it enables marketplaces like OpenSea to support an infinite variety of distinct items using a single architecture.
Explain Like I'm 12
ERC-721 is for items that are one-of-a-kind. Think of it like a trading card game where every card has a unique serial number. Unlike coins in your pocket that are all the same, these tokens are unique and cannot be swapped one-for-one.
Why It Matters
It created the digital collectibles and NFT market. It allows for provable scarcity and ownership of unique digital property.
How It Works
Similar to ERC-20, it uses a smart contract interface, but it maps a unique `tokenId` to a specific owner address. It includes functions to transfer ownership of a specific item and query who owns a specific unique asset. The metadata associated with the token can point to off-chain data like images or descriptions.
Real-World Example
CryptoPunks and Bored Ape Yacht Club are iconic collections built on the ERC-721 standard.
Advantages
- Verifiable digital ownership
- Unique asset representation
- Interoperable with NFT marketplaces
Limitations
- High gas for minting
- Data storage scalability
Common Misconceptions
- People think all NFTs must be pictures, but they can be any digital identity or asset.
- Many believe NFTs themselves are stored on-chain, but often only the metadata reference is.
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Related Terms
Metadata
Metadata in the context of NFTs refers to the descriptive data that defines the characteristics, traits, and visual identity of a token. This data is usually stored in a JSON file format and links the blockchain token ID to external assets such as image files, animations, or audio. The metadata dictates the unique attributes of the NFT, such as 'color', 'background', or 'power level', which determine its rarity within a collection and how it is rendered in applications or galleries.
Smart Contract
A smart contract is a self-executing program stored on a blockchain that automatically runs when predetermined conditions are met. These contracts eliminate the need for intermediaries by encoding terms directly into lines of code, ensuring that the agreement is enforced exactly as written without human interference. Because they reside on an immutable ledger, the execution results are verifiable, transparent, and impossible to tamper with once deployed.
Smart Contract
A self-executing program stored on a blockchain that automatically enforces and executes the terms of an agreement when predetermined conditions are met. Smart contracts are deterministic, immutable once deployed, and form the backbone of decentralized applications.
Burn Address
A burn address is a public address that lacks a corresponding private key, making any assets sent to it permanently inaccessible. Because there is no private key to generate a signature for an outgoing transaction, any tokens transferred to this address are effectively removed from the circulating supply. This mechanism is frequently used in 'token burns' to reduce supply, control inflation, or prove the destruction of assets, such as wrapping tokens or finalizing cross-chain bridge migrations.
EIP
An EIP (Ethereum Improvement Proposal) is a formal design document that provides information to the Ethereum community or describes a new feature for the Ethereum protocol, its client APIs, or contract standards. EIPs are the primary mechanism for proposing changes to Ethereum, following a rigorous peer-review and consensus process. They ensure that changes to the protocol are vetted by the community, developers, and researchers before being implemented through a hard fork or network upgrade.
ERC-1155
ERC-1155 is a multi-token standard that allows a single smart contract to manage both fungible (like currencies) and non-fungible (like unique items) tokens simultaneously. This standard is highly gas-efficient because it allows for batch transfers of multiple tokens in a single transaction. It is widely used in gaming and complex dApps where a user might need to hold thousands of different items, such as weapons, health potions, and currency, all within one inventory system governed by a single contract.