Exploring Web3 Opcodes: The Building Blocks of Decentralized Applications

Exploring Web3 Opcodes: The Building Blocks of Decentralized Applications https://celo.academy/uploads/default/optimized/2X/0/0d9ee8d16db636feb02c2b872d77c1210a8a5d4b_2_1024x576.png
none 0.0 0


The emergence of Web3 has revolutionized the internet by introducing decentralized technologies and platforms that empower users with greater control, privacy, and security. At the heart of Web3 lies a powerful concept known as opcodes. These opcodes form the building blocks of smart contracts, decentralized applications (dApps), and blockchain networks, enabling a wide array of functionalities and interactions.

Web3 Opcodes are the low-level instructions that are used by the Ethereum Virtual Machine (EVM) to execute smart contracts on the Ethereum blockchain.
Opcodes are executed in sequence, and each opcode consumes a certain amount of gas. Gas is a unit of computation that is used to pay for the execution of code on the EVM. The more complex an opcode, the more gas it will consume. There are currently 256 opcodes, each of which performs a specific operation. Examples Opcodes are STOP, ADD, SUB, MUL, DIV, SDIV, MOD, SMOD, MULMOD, CALL, SLOAD, SSTORE etc.

In this article, we will delve into the world of Web3 opcodes, understanding their significance, and exploring some of the key opcodes that drive this new decentralized landscape.


In this article, we will be discussing Opcodes which are the building blocks of decentralized applications hence a basic knowledge of Blockchain is and smart contracts is needed.

For the purpose of this article, we will focus on the key Web3 Opcodes:

Key web3 opcodes


The CREATE opcode is a fundamental instruction in the Web3 ecosystem that enables the creation and deployment of new smart contracts on the blockchain.

When a CREATE opcode is executed, it takes as input the bytecode of the contract to be deployed. The bytecode represents the compiled form of the contract’s source code. The CREATE opcode then deploys this bytecode to the blockchain, resulting in the creation of a new contract instance with a unique address.

The deployment of a contract through the CREATE opcode involves several steps:

  • Compilation: The contract’s source code is compiled into bytecode, which is a low-level representation of the contract’s instructions and data.
    Transaction Creation: A transaction is created that includes the CREATE opcode, along with the bytecode of the contract to be deployed as part of its data field.
  • Transaction Execution: The transaction containing the CREATE opcode is sent to the blockchain network for execution.
  • Contract Creation: When the transaction is processed by the network, the CREATE opcode is executed by the blockchain’s virtual machine. It initializes a new contract instance using the provided bytecode and assigns a unique address to it.
  • Contract Initialization: After the contract is created, its constructor function is executed to initialize any initial state variables and perform any required setup.


The CALL opcode is a crucial instruction in the Web3 ecosystem that facilitates the interaction between smart contracts and external addresses. It enables interaction between contracts, facilitating functions calls and data exchange. It enables the invocation of functions in other contracts or the communication with externally owned accounts (EOAs).

When the CALL opcode is executed, it triggers the following actions:

  • Address and Data Specification: The CALL opcode requires specifying the target address and the data to be passed along with the call. The target address can be either the address of another smart contract or an externally owned account.
  • Function Invocation: If the target address corresponds to a smart contract, the CALL opcode can invoke a specific function within that contract.
  • State Modification and Value Transfer: The CALL opcode can modify the state of the target contract by executing the specified function.
  • Gas Consumption and Return Value: The CALL opcode consumes gas, which represents the computational resources required to execute the function call. Gas ensures that the executing contract or account covers the cost of computation.

The CALL opcode enables various interactions and functionalities within the Web3 ecosystem which includes:

  • Contract Interactions: Smart contracts can invoke functions in other contracts using the CALL opcode.
  • Data Exchange: The CALL opcode enables the passing of data between contracts. It allows contracts to exchange information, trigger specific actions, or retrieve data from other contracts.
  • Value Transfers: Alongside function invocation, the CALL opcode enables the transfer of ether (cryptocurrency) from one contract or account to another. This feature facilitates financial transactions and the exchange of value within the Web3 ecosystem.
  • Oracles and External Systems: The CALL opcode allows smart contracts to interact with external systems or oracles. Oracles provide external data to smart contracts, enabling the utilization of real-world information within the blockchain.


The SSTORE opcode is used to store a value at a specific storage slot within a smart contract. It takes two inputs: the storage slot and the value to be stored.

The storage slot is typically represented by a 256-bit key, and the associated value can be of various types, including integers, addresses, or complex data structures.

When the SSTORE opcode is executed, it updates the state of the contract by persistently storing the provided value at the specified storage slot. This stored value can be accessed later using the SLOAD opcode.


The SLOAD opcode is used to retrieve the value stored at a specific storage slot within a smart contract. It takes the storage slot as input and returns the corresponding value that was previously stored using the SSTORE opcode.

When the SLOAD opcode is executed, it reads the stored value from the contract’s storage space and makes it available for further use within the contract’s execution.

The combination of SSTORE and SLOAD opcodes provides a mechanism for persistent data storage within smart contracts. By utilizing these opcodes, dApps can store and retrieve information in a decentralized and tamper-resistant manner.

The SSTORE and SLOAD opcodes are particularly useful for:

  • Maintaining Contract State: Smart contracts often need to maintain and update their internal state. The SSTORE opcode allows contracts to store values that represent the current state, enabling contract-level variables and data persistence.
  • Data Sharing and Communication: Contracts can share data with each other by storing information using SSTORE and allowing other contracts to read that information using SLOAD. This facilitates inter-contract communication and coordination within a decentralized system.
  • Efficient Data Access: The use of storage slots and efficient key-value retrieval with SSTORE and SLOAD opcodes enables contracts to access stored data quickly and efficiently, enhancing the overall performance of the dApp.
  • Decentralized Databases: SSTORE and SLOAD provide the foundation for decentralized databases built on the blockchain. By leveraging these opcodes, developers can create decentralized applications that store and retrieve data securely and reliably.


The JUMP opcode performs an unconditional jump to a specific location within the contract’s bytecode. It takes a destination point or a jump target as input, specifying the location to which the program flow should be transferred.

When the JUMP opcode is executed, the contract’s execution immediately moves to the specified destination point in the bytecode, allowing for non-linear execution paths.


The JUMPI opcode performs a conditional jump based on a given condition. It takes two inputs: a jump target and a condition. If the condition evaluates to true, the program flow transfers to the specified jump target. If the condition is false, the execution continues with the next instruction in the bytecode.
Both JUMP and JUMPI opcodes are used to control the execution flow within smart contracts, enabling the implementation of various control structures, including loops, conditionals, and branching logic. These opcodes empower developers to create smart contracts with sophisticated logic and automate complex processes.

Use cases for JUMP and JUMPI opcodes include:

  • Looping Constructs: By using JUMP and JUMPI opcodes in combination with counters or condition checks, developers can implement loops within smart contracts. Loops allow for repetitive execution of code, iterating over collections of data or performing operations a specific number of times.
  • Conditional Statements: The JUMPI opcode enables the implementation of if-else statements and conditional logic within smart contracts. Based on the evaluation of a condition, the program flow can be directed to different sections of code, allowing for decision-making and dynamic behavior.
  • Exception Handling: JUMP and JUMPI opcodes are crucial for exception handling within smart contracts. By using these opcodes, developers can define error conditions and specify where the execution flow should jump in case an exception occurs. This allows for graceful error handling and rollback of transactions when necessary
  • Program Modularity: JUMP and JUMPI opcodes contribute to the modularity and composability of smart contracts. By enabling jumps to different parts of the bytecode, contracts can call and reuse functions defined at various locations within the contract, promoting code reuse and reducing code duplication.


The REVERT opcode is an important instruction in the Web3 ecosystem that allows smart contracts to gracefully revert the state of a transaction when an error or exception occurs during execution. It is used to indicate that the current transaction has failed and should be rolled back, allowing the user to recover their funds and preventing them from being lost irretrievably.

When a smart contract encounters an error during execution, it can use the REVERT opcode to revert the state of the transaction to the previous state and return any remaining gas to the user. The REVERT opcode takes two inputs: a memory offset and a length. The memory offset indicates the location in memory where the error message is stored, and the length specifies the length of the error message in bytes.

If the REVERT opcode is executed, the transaction’s status is set to “failed,” and any remaining gas is returned to the user. The error message specified by the memory offset and length is also included in the transaction’s output, allowing users to understand why the transaction failed and take appropriate action.

Some use cases for the REVERT opcode include:

  • Input Validation: Smart contracts often rely on user input to execute their logic. The REVERT opcode can be used to validate user input and reject invalid inputs, preventing the contract from executing in an unintended way.
  • Exception Handling: The REVERT opcode is critical for handling exceptions and errors within smart contracts. It allows contracts to handle unexpected conditions gracefully and return meaningful error messages to users, reducing the risk of funds being lost irretrievably.
  • Security: The REVERT opcode is an essential security mechanism for smart contracts. It prevents malicious actors from exploiting vulnerabilities in the contract code and stealing funds by reverting the state of the transaction when an error or exception occurs.


The EXTCODESIZE opcode retrieves the size of the code associated with an external contract. It takes an address as input and returns the size of the code in bytes. The EXTCODESIZE opcode allows contracts to determine the size of the bytecode of other contracts on the blockchain.
By using EXTCODESIZE, a contract can check the existence and presence of code at a specific address. This information is useful for contract-to-contract communication and can be used to verify that an address corresponds to a deployed contract.


The EXTCODECOPY opcode is used to copy the code from an external contract into the memory of the calling contract. It takes three inputs: the address of the external contract, the memory offset within the calling contract’s memory where the code will be copied, and the length of the code to be copied.

The EXTCODECOPY opcode allows contracts to retrieve the bytecode of other contracts on the blockchain. This bytecode can then be analyzed, processed, or used for various purposes within the executing contract. For example, a contract may inspect the bytecode of another contract to verify its functionality or extract specific data from it.

EXTCODESIZE and EXTCODECOPY opcodes provide functionality for smart contracts to retrieve code from other contracts and interact with them within the Web3 ecosystem.

By utilizing EXTCODESIZE and EXTCODECOPY opcodes, developers can implement a range of functionalities within Web3 applications:

  • Contract Analysis: The EXTCODESIZE and EXTCODECOPY opcodes enable contract code analysis and verification. Contracts can inspect the bytecode of other contracts to ensure their security, validate their functionality, or perform audits.
  • Contract Interactions: The opcodes allow contracts to communicate and interact with each other. By retrieving the bytecode of another contract, a contract can understand its interface, invoke its functions, or extract relevant data from it.
  • Decentralized Application Interoperability: The EXTCODESIZE and EXTCODECOPY opcodes facilitate interoperability among dApps. Contracts can analyze and interact with other contracts within the ecosystem, allowing for composability and the creation of complex decentralized systems.
  • Smart Contract Upgrades: The opcodes can be used in contract upgrade scenarios. A contract can retrieve the bytecode of a new version of a contract and validate its compatibility or perform a migration process based on the code analysis.


The DELEGATECALL opcode is a powerful instruction in the Web3 ecosystem that enables smart contracts to execute code in another contract’s context. It provides a mechanism for smart contracts to delegate the execution of a function to another contract, while still maintaining their own state and context.

The DELEGATECALL opcode works by passing a message to the specified contract, which executes the requested function as if it were part of its own code. The opcode then returns any data returned by the function. Importantly, the state of the original contract is preserved, and any changes made to the state by the called contract are made in the context of the calling contract.

The DELEGATECALL opcode takes three inputs: the gas limit, the contract address, and the function signature and arguments to be executed. The gas limit specifies the maximum amount of gas that can be used in the execution of the function, protecting the caller from out-of-gas errors or attacks.

Use cases for the DELEGATECALL Opcode include:

  • DELEGATECALL is often used in contract composition, where a contract delegates part of its functionality to another contract. For example, a contract might use DELEGATECALL to execute a library function implemented in a separate contract, rather than including the library code in its own bytecode. This approach can reduce code duplication, simplify contract design, and improve contract upgradability.

  • DELEGATECALL can also be used to create complex contract systems, where contracts interact with each other and delegate certain tasks to specialized contracts. For instance, a voting contract may use DELEGATECALL to call a counting contract that tallies the votes, ensuring the voting contract remains focused on its specific functionality.

However, the DELEGATECALL opcode can also introduce security risks, and careful consideration must be given to its use. Since the called contract executes in the context of the calling contract, it has access to the calling contract’s state and can potentially modify it. Malicious code executed by the called contract can also lead to reentrancy attacks, where the called contract repeatedly calls back into the calling contract, potentially draining its funds or causing unexpected behavior.

Examples of smart contracts where these Opcodes can be used include:


A crowdfunding contract: A contract where each contribution creates a new contract to represent a unique campaign.

Token Factory: A contract that enables users to create their own custom tokens by deploying new token contracts through the CREATE opcode.

Escrow Factory: A contract that allows users to create new escrow contracts dynamically using the CREATE opcode.


Decentralized Exchange: A contract that facilitates token swaps by calling the functions of other contracts, such as transferring tokens and updating balances.

Multi-signature Wallet: A contract that allows multiple owners to manage funds by calling the contract’s functions to approve and execute transactions.


Voting Contract: A contract that stores votes and other relevant information using SSTORE and retrieves them using SLOAD.

Auction Contract: A contract that uses SSTORE and SLOAD to store and retrieves bidding information, including the highest bid and bidder details.


Crowdfunding Contract: A contract that uses JUMP and JUMPI to handle different stages of a crowdfunding campaign, such as transitioning from a funding stage to a refund stage if the funding goal is not met.


Proxy Contract: A contract that uses EXTCODECOPY and EXTCODESIZE to interact with an external contract dynamically, allowing the proxy contract to delegate function calls to the external contract.


Upgradeable Contract: A contract that utilizes DELEGATECALL to enable contract upgrades while preserving the state and functionality of the existing contract.

Next steps

With this knowledge, you can go on and maximize the utility of the key Web3 Opcodes.


These opcodes provide the necessary functionality for deploying, interacting with, and managing smart contracts. Developers working with Web3 technologies need to have a solid understanding of opcodes to effectively build and interact with decentralized applications. By leveraging the power of Web3 opcodes, developers can create sophisticated and autonomous applications that leverage the decentralized and trustless nature of blockchain networks.

About the author

Okoro Samuel Ogheneyole is a Web3 technical writer who has burning passion for technology and loves to share his knowledge for the benefit of other Web3 enthusiasts.



Approved for you to get started. You can manage the tutorial here by changing the category to Proposals > In Progress then Proposals > Review as you complete the tutorial. Thanks!

1 Like

I’m done working on this topic but I’m having difficulty editing this page to post my work. I would appreciate if the problem is rectified. Thank you.


Looks great so far! I cleaned up the formatting a bit for readability and your reviewer will help with the rest. :slight_smile:


Thank you so much. I appreciate


i will be reviewing this.

1 Like

i have fixed the markdown where it was need other than that post looks quite good. can you add a smart contract by use these opcodes as example? and add that in post?


Noted. I will work on it. Thank you.


Done. Thank you very much Sir.


Approved @Kunaldawar


This is a well articulated content , welldone brother.


Is accessing medium.org everyone’s issue or just me?


Please fix the link

Thanks for the good work.

1 Like