What is metadata in blockchain transactions?

Metadata in blockchain refers to additional information or data that can be associated with transactions or other elements on a blockchain network.

Metadata in blockchain transactions, explained

Additional data or information that can be appended to a crypto transaction on a blockchain is referred to as metadata in blockchain transactions.

Although the main function of a blockchain is to document and authenticate the transfer of digital assets, including cryptocurrencies like Ether (ETH) or Bitcoin (BTC), metadata enables users to add additional information or context to their transactions. 

Metadata is data about data. In the context of blockchain transactions, it includes information that is not directly related to the transfer of cryptocurrency but can provide additional functionality to the transaction.

There are two main types of metadata in blockchain transactions:

On-chain metadata

Since this metadata is immediately stored on the blockchain, it is part of the transaction data that is stored there. Anyone with access to the blockchain can see it. Information such as transaction labels, notes or references to external contracts or documents can all be found in on-chain metadata.

Off-chain metadata

This data is referenced in the transaction but is not kept on the blockchain directly. Links to other content, such as files, documents or web URLs that provide further details about the transaction, can be included in off-chain metadata. Off-chain metadata is a tool that users can utilize to reduce clutter on the blockchain.

How on-chain and off-chain metadata are stored

On-chain metadata, such as transaction details, smart contract code and token properties, is integral to the blockchain’s data structure, being permanently stored and replicated across network nodes. In contrast, off-chain metadata is stored externally, using cryptographic references, enhancing blockchain efficiency and flexibility.

The blockchain’s data structure contains on-chain metadata natively. This information is permanently saved and replicated across all network nodes, and it forms a component of the blockchain’s ledger. The majority of on-chain metadata is kept within the actual transactions. On the blockchain, every transaction has a payload with pertinent metadata. For instance, the sender, receiver, amount and transaction date are recorded as on-chain metadata when sending cryptocurrency between addresses.

When it comes to smart contracts, the contract’s code and accompanying data are kept on the blockchain as on-chain metadata. This covers the functions, state variables and related data of the contract. Each block has headers that provide certain metadata that is easily accessible for verification, like block timestamps, block numbers and transaction IDs. Metadata regarding token properties (e.g., token name, symbol, supply) is frequently maintained on the blockchain for tokens like Ethereum’s ERC-721 and ERC-20.

In contrast, off-chain metadata is stored off the blockchain. It can be kept in a variety of places, including off-chain scaling solutions like the Lightning Network, decentralized storage systems like the InterPlanetary File System (IPFS), and external databases. Blockchain uses cryptographic hashes or pointers to refer to off-chain metadata, which frees up space on the blockchain for larger or less important data storage, lessens congestion and provides flexibility to applications that need private or dynamic information.

Examples of metadata in blockchain transactions

Metadata in blockchain includes timestamps, transaction details, smart contract data, digital signatures, gas fees, IPFS links, oracles’ information and nonfungible token (NFT) metadata, enabling diverse functionalities and information storage within the blockchain network.


A blockchain’s blocks each contain a timestamp that shows the moment the block was added to the chain. The timing of a transaction is recorded via this metadata.

Transaction details

Sender and recipient addresses, transaction amounts and distinct transaction IDs are just a few examples of the metadata that can be included with each transaction on a blockchain.

Smart contract data

Parameters and input data required for the contract’s operation may be included in the metadata when smart contracts are executed on a blockchain.

Digital signatures

To confirm the legitimacy of transactions and demonstrate ownership, metadata contains digital signatures.

Gas fees

On blockchains like Ethereum, metadata may include details regarding the gas fees associated with processing transactions. Miners and validators need this information in order to prioritize transactions.

InterPlanetary File System links

Links to IPFS, a decentralized file storage system, can be found in blockchain metadata. Users can access the data on the blockchain by retrieving a reference, usually in the form of a hash, to the IPFS file as needed. Large files, including images, videos or documents related to on-chain assets like NFTs, can be stored using this method.


Oracles are external services that provide smart contracts access to real-world data. These oracles’ information may be included in blockchain metadata to cause smart contract activities.

Nonfungible token metadata

NFTs often contain metadata, such as creators, descriptions and other details about the digital or physical assets they represent.

How to add metadata to a blockchain transaction?

When a user wants to add metadata to a blockchain transaction, they can do so through a smart contract, which is a self-executing contract with predetermined terms encoded into it.

Let’s understand the process using Ethereum as an example, which is known for its ability to include metadata in transactions through smart contracts.

Create a smart contract

A smart contract must be created before metadata can be added. Instructions on where and how the metadata will be stored are included in this contract. The metadata can be stored in a variable that is defined, usually as a string. Here is a simplified example written in Solidity, the

How to store metadata securely on the blockchain with MyContract

In the above example, the smart contract called MyContract has a publicly readable metadata variable and features a function called setMetadata that enables the metadata to be updated.

Interacting with the smart contract

An individual must communicate with the smart contract by sending a transaction to add metadata to a blockchain transaction. This can be done using libraries like web3.js or ethers.js, or via Ethereum wallet applications. 

Verifying the metadata

By interacting with the smart contract and reading the metadata variable, anyone can validate the metadata once the transaction has been confirmed and added to the blockchain. However, it’s crucial to remember that considerations such as gas costs, security and privacy should be considered while adding metadata to a blockchain transaction.

Use cases of blockchain metadata

Blockchain metadata finds application in a wide range of industries, including supply chain management, digital identity, smart contracts, NFTs and healthcare.

Supply chain management

Businesses can improve traceability and transparency by putting product production, transportation and quality-related metadata on a blockchain. A food producer, for example, can keep track of information regarding the provenance of materials, their passage through the supply chain and quality checks. 

This information is essential for addressing problems like fraud or recalls, guaranteeing regulatory compliance and confirming authenticity. Furthermore, customers can use this metadata to make well-informed decisions regarding the goods they purchase.

Digital identity and authentication

Blockchain metadata can be used to safely manage and preserve credentials and personal data. People are in charge of their data and can allow or prohibit access to those who are allowed, which lowers the possibility of identity theft and privacy violations. Enterprises, governments and educational institutions can use this technology to improve service security and expedite identification verification procedures.

Smart contracts

Another domain in which blockchain metadata is essential is smart contracts. Metadata is used by these self-executing contracts to decide when and how to execute a particular condition. An insurance smart contract, for example, could use meteorological data as metadata to immediately initiate payouts for policyholders impacted by unfavorable weather conditions. 

In the financial industry, loan agreements can establish eligibility and interest rates based on credit ratings and transaction history that are maintained as metadata, allowing for more automated and efficient lending procedures.

Nonfungible tokens and digital assets

NFTs and digital assets frequently use blockchain information to provide digital collectibles, artwork and assets meaning and value. Information about the originator, the history of ownership and the characteristics of the digital item are examples of metadata. Provenance tracking, art authentication and the creation of decentralized applications (DApps) that build upon NFTs can all benefit greatly from this knowledge.

Healthcare records and data security

Furthermore, the healthcare sector is using blockchain metadata to manage patient records securely and guarantee data integrity. Medical histories, patient consent forms and data access logs can all be stored in metadata, improving the security and privacy of health information. Furthermore, it facilitates communication between various healthcare systems and allows emergency responders to obtain vital medical information more quickly.

Challenges associated with blockchain metadata

Overcoming challenges in blockchain metadata, including scalability issues, data security concerns and oracle reliability, is essential for sustainable technology advancement and widespread adoption.

Concerns about scalability and storage costs are important because, as blockchain networks grow in size, they can become less effective and need more resources. Large volumes of data storage on the blockchain may strain network architecture and increase the risk of centralization.

Another issue is data security and privacy, particularly when dealing with private or sensitive data. Blockchain’s transparency may contradict privacy regulations, so implementation and design must be done carefully. Furthermore, the reliability of blockchain applications and smart contracts may be impacted by malicious or erroneous data inputs when depending on oracles to retrieve external data.

Addressing these challenges is crucial for the continued development and adoption of blockchain technology in various industries. Overcoming these obstacles in blockchain metadata calls for a diversified strategy. Developers can explore layer-2 solutions and sharding techniques to offload certain data from the main chain to avoid scalability difficulties. 

Encryption and permissioned blockchains can be used to improve data security and privacy for sensitive data. Oracle reliability can be ensured by employing multiple data sources for validation and reputation mechanisms. Hence, blockchain metadata may be made more efficient and secure with the help of strong security protocols, inventive technology and careful design.