Metadata
Last Updated: October 29, 2026
Quick Answer: Metadata is data that describes other data. In crypto, it most often means the information that tells wallets and marketplaces what a token is: an NFT’s name, description, image link and traits, usually stored in a JSON file that the token’s smart contract points to. Metadata can live on-chain, inside the blockchain itself, or off-chain on a server or storage network such as IPFS, and where it lives decides how permanent and tamper-resistant it is.
Key Takeaways
- Metadata gives digital assets context: without it, an NFT is only a token ID and an owner address
- ERC-721 and ERC-1155, Ethereum’s main NFT standards, define an optional metadata function that returns a URI pointing to a JSON file
- On-chain metadata is stored on the blockchain and is as permanent as the chain; off-chain metadata is cheaper but depends on whoever hosts the file
- Blockchains also carry transaction metadata, such as Bitcoin’s OP_RETURN data and Cardano’s labeled metadata
- Public metadata, including timestamps, addresses and amounts, can reveal a lot about users, which is why privacy tools focus on it
What Metadata Means in Crypto
The general definition is simple: metadata is “data about data.” A photo’s file size, date and camera model are metadata about the image. On a blockchain, the same idea applies at two levels: metadata that describes an asset, such as an NFT, and metadata attached to or produced by transactions.
Asset metadata matters because blockchains are expensive places to store data. Instead of writing a full image into a smart contract, most collections store a short link on-chain and keep the descriptive file elsewhere. Marketplaces, wallets and block explorers read that file to show the item’s name, picture and attributes.
NFT Metadata and Token Standards
ERC-721
The ERC-721 standard, created in January 2018 and marked Final, includes an optional metadata extension with three functions: name() and symbol() for the collection, and tokenURI(), which returns “a distinct Uniform Resource Identifier (URI) for a given asset.” The standard says that URI “may point to a JSON file” following its metadata schema, which has three core fields:
| Field | Meaning in the standard |
|---|---|
| name | Identifies the asset the NFT represents |
| description | Describes the asset |
| image | A URI pointing to an image file representing the asset |
Marketplaces commonly add fields such as attributes (traits), animation_url and external_url. The standard also says the URI “MAY be mutable,” meaning a project can change what a token points to unless the contract prevents it.
ERC-1155
ERC-1155, the multi-token standard created in June 2018, uses a single uri() function for all token IDs. Clients replace an {id} placeholder in the URI with the token ID written as 64 lowercase hexadecimal characters, so one template can serve thousands of items. Its JSON schema adds fields including decimals, properties and localization, and the contract must emit a URI event when a token’s link changes, unless the change is dynamic or programmatic.
Metadata Updates and Other Chains
EIP-4906, a Final extension to ERC-721 from 2022, adds MetadataUpdate and BatchMetadataUpdate events so marketplaces know when to refresh NFT data. Other chains follow similar patterns. On Solana, Metaplex’s Token Metadata program stores the name, a URI to an off-chain JSON file and creator shares in an on-chain account, and an “Is Mutable” setting can lock them permanently. Metaplex now calls it a legacy program and recommends its newer Metaplex Core standard for new projects. On Cardano, the CIP-25 standard attaches NFT metadata directly to the minting transaction under metadata label 721.
On-Chain vs Off-Chain Metadata
| On-chain | Off-chain (IPFS, Arweave) | Off-chain (regular server) | |
|---|---|---|---|
| Where data lives | In the contract or transaction | Content-addressed storage network | A company’s web server |
| Can it change? | Only as the contract allows | No, a new file means a new address | Yes, at any time |
| Main risk | High storage cost | Files lost if no one pins or pays to store them | Server shutdown or silent edits |
| Typical use | Small generative art, on-chain games | Most NFT collections | Games, dynamic or test projects |
IPFS is the most common off-chain choice for NFTs because each file’s address is derived from its content. The IPFS documentation recommends ipfs:// links rather than gateway URLs, and it recommends following the ERC-721 and ERC-1155 schemas so wallets can read the files. An NFT whose metadata sits on a server that goes offline can lose its image and traits, even though the token itself still exists on the blockchain.
Transaction Metadata
Transactions can carry extra data too. Bitcoin’s OP_RETURN outputs let users embed small amounts of data in a transaction. Bitcoin Core 30.0, released on October 10, 2025, raised its default relay limit for this data to 100,000 bytes, which the release notes say “effectively uncaps the limit,” and allowed multiple OP_RETURN outputs. Node operators can still revert to the earlier 83-byte setting. Bitcoin Core 31.0, released in April 2026, kept this default. Cardano supports labeled transaction metadata natively, and on Ethereum, the input data of a transaction records which contract function was called and with what parameters.
Metadata and Privacy
On public blockchains, transaction metadata is visible to everyone: sending and receiving addresses, amounts, timestamps, fees and the contracts involved. Analytics firms combine these details with off-chain information, such as exchange records or IP addresses seen by network nodes, to link addresses to people. Regulations such as the crypto Travel Rule add another layer: exchanges must send customer names and account details alongside transfers, and that information is kept off-chain between providers.
For NFT holders, metadata can also reveal more than expected, since anything placed in a public JSON file or on IPFS can be read and copied by anyone.
Frequently Asked Questions
What is metadata in crypto?
Metadata is data that describes other data. In crypto it usually means the details that explain what a token or transaction is, such as an NFT’s name, description, image link and traits, or extra data attached to a transaction. Wallets, marketplaces and block explorers read this information to display assets correctly, since the token alone is just an ID and an owner address.
Where is NFT metadata stored?
Most NFTs store only a link on the blockchain. The tokenURI or uri function returns an address pointing to a JSON file, which is often hosted on IPFS or Arweave and sometimes on a regular web server. Some collections store everything on-chain, which costs more but removes dependence on outside storage. You can check where a token’s metadata lives through a block explorer.
Can NFT metadata be changed after minting?
It depends on the contract and storage. ERC-721 allows the token URI to be mutable, so a project can point it elsewhere unless the code prevents that. Files on IPFS cannot be edited without changing their address, while files on ordinary servers can be changed at any time. On Solana, setting Is Mutable to false permanently locks the main fields.
What is the difference between on-chain and off-chain metadata?
On-chain metadata is written directly into the blockchain, so it lasts as long as the chain and cannot be removed by a third party, but storage is expensive. Off-chain metadata is kept outside the chain, on a storage network or server, and linked from the token. It is cheaper, but its availability depends on whoever hosts or pins the files.
Data sources: Ethereum Improvement Proposals EIP-721, EIP-1155 and EIP-4906 (eips.ethereum.org); Cardano CIP-25; Metaplex Token Metadata documentation; Bitcoin Core 30.0 and 31.0 release notes; IPFS documentation. Checked October 29, 2026.