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Learn about the differences between smart contracts and a FRAME-based runtime. They are both “code stored onchain”, but how do they differ?

§Runtime vs. Smart Contracts

TL;DR: If you need to create a Blockchain, then write a runtime. If you need to create a DApp, then write a Smart Contract.

This is a comparative analysis of Substrate-based Runtimes and Smart Contracts, highlighting their main differences. Our aim is to equip you with a clear understanding of how these two methods of deploying on-chain logic diverge in their design, usage, and implications.

Both Runtimes and Smart Contracts serve distinct purposes. Runtimes offer deep customization for blockchain development, while Smart Contracts provide a more accessible approach for decentralized applications. Understanding their differences is crucial in choosing the right approach for a specific solution.


Substrate is a modular framework that enables the creation of purpose-specific blockchains. In the Polkadot ecosystem you can find two distinct approaches for on-chain code execution: Runtime Development and Smart Contracts.

§Smart Contracts in Substrate

Smart Contracts are autonomous, programmable constructs deployed on the blockchain. In FRAME, Smart Contracts infrastructure is implemented by the pallet_contracts for WASM-based contracts or the pallet_evm for EVM-compatible contracts. These pallets enable Smart Contract developers to build applications and systems on top of a Substrate-based blockchain.

§Runtime in Substrate

The Runtime is the state transition function of a Substrate-based blockchain. It defines the rules for processing transactions and blocks, essentially governing the behavior and capabilities of a blockchain.

§Comparative Table

| Aspect | Runtime | Smart Contracts | |———————–|———————————————————————––|–––––––––––––––––––––––––––––––––––| | Design Philosophy | Core logic of a blockchain, allowing broad and deep customization. | Designed for DApps deployed on the blockchain runtime.| | Development Complexity | Requires in-depth knowledge of Rust and Substrate. Suitable for complex blockchain architectures. | Easier to develop with knowledge of Smart Contract languages like Solidity or ink!. | | Upgradeability and Flexibility | Offers comprehensive upgradeability with migration logic and on-chain governance, allowing modifications to the entire blockchain logic without hard forks. | Less flexible in upgrade migrations but offers more straightforward deployment and iteration. | | Performance and Efficiency | More efficient, optimized for specific needs of the blockchain. | Can be less efficient due to its generic nature (e.g. the overhead of a virtual machine). | | Security Considerations | Security flaws can affect the entire blockchain. | Security risks usually localized to the individual contract. | | Weighing and Metering | Operations can be weighed, allowing for precise benchmarking. | Execution is metered, allowing for measurement of resource consumption. |

We will now explore these differences in more detail.

§Design Philosophy

Runtimes and Smart Contracts are designed for different purposes. Runtimes are the core logic of a blockchain, while Smart Contracts are designed for DApps on top of the blockchain. Runtimes can be more complex, but also more flexible and efficient, while Smart Contracts are easier to develop and deploy.

§Runtime Design Philosophy
  • Core Blockchain Logic: Runtimes are essentially the backbone of a blockchain. They define the fundamental rules, operations, and state transitions of the blockchain network.
  • Broad and Deep Customization: Runtimes allow for extensive customization and flexibility. Developers can tailor the most fundamental aspects of the blockchain, like introducing an efficient transaction fee model to eliminating transaction fees completely. This level of control is essential for creating specialized or application-specific blockchains.
§Smart Contract Design Philosophy
  • DApps Development: Smart contracts are designed primarily for developing DApps. They operate on top of the blockchain’s infrastructure.
  • Modularity and Isolation: Smart contracts offer a more modular approach. Each contract is an isolated piece of code, executing predefined operations when triggered. This isolation simplifies development and enhances security, as flaws in one contract do not directly compromise the entire network.

§Development Complexity

Runtimes and Smart Contracts differ in their development complexity, largely due to their differing purposes and technical requirements.

§Runtime Development Complexity
  • In-depth Knowledge Requirements: Developing a Runtime in Substrate requires a comprehensive understanding of Rust, Substrate’s framework, and blockchain principles.
  • Complex Blockchain Architectures: Runtime development is suitable for creating complex blockchain architectures. Developers must consider aspects like security, scalability, and network efficiency.
§Smart Contract Development Complexity
  • Accessibility: Smart Contract development is generally more accessible, especially for those already familiar with programming concepts. Knowledge of smart contract-specific languages like Solidity or ink! is required.
  • Focused on Application Logic: The development here is focused on the application logic only. This includes writing functions that execute when certain conditions are met, managing state within the contract, and ensuring security against common Smart Contract vulnerabilities.

§Upgradeability and Flexibility

Runtimes and Smart Contracts differ significantly in how they handle upgrades and flexibility, each with its own advantages and constraints. Runtimes are more flexible, allowing for writing migration logic for upgrades, while Smart Contracts are less flexible but offer easier deployment and iteration.

§Runtime Upgradeability and Flexibility
  • Migration Logic: One of the key strengths of runtime development is the ability to define migration logic. This allows developers to implement changes in the state or structure of the blockchain during an upgrade. Such migrations can adapt the existing state to fit new requirements or features seamlessly.
  • On-Chain Governance: Upgrades in a Runtime environment are typically governed on-chain, involving validators or a governance mechanism. This allows for a democratic and transparent process for making substantial changes to the blockchain.
  • Broad Impact of Changes: Changes made in Runtime affect the entire blockchain. This gives developers the power to introduce significant improvements or changes but also necessitates a high level of responsibility and scrutiny, we will talk further about it in the Security Considerations section.
§Smart Contract Upgradeability and Flexibility
  • Deployment and Iteration: Smart Contracts, by nature, are designed for more straightforward deployment and iteration. Developers can quickly deploy contracts.
  • Contract Code Updates: Once deployed, although typically immutable, Smart Contracts can be upgraded, but lack of migration logic. The pallet_contracts allows for contracts to be upgraded by exposing the set_code dispatchable. More details on this can be found in Ink! documentation on upgradeable contracts.
  • Isolated Impact: Upgrades or changes to a smart contract generally impact only that contract and its users, unlike Runtime upgrades that have a network-wide effect.
  • Simplicity and Rapid Development: The development cycle for Smart Contracts is usually faster and less complex than Runtime development, allowing for rapid prototyping and deployment.

§Performance and Efficiency

Runtimes and Smart Contracts have distinct characteristics in terms of performance and efficiency due to their inherent design and operational contexts. Runtimes are more efficient and optimized for specific needs, while Smart Contracts are more generic and less efficient.

§Runtime Performance and Efficiency
  • Optimized for Specific Needs: Runtime modules in Substrate are tailored to meet the specific needs of the blockchain. They are integrated directly into the blockchain’s core, allowing them to operate with high efficiency and minimal overhead.
  • Direct Access to Blockchain State: Runtime has direct access to the blockchain’s state. This direct access enables more efficient data processing and transaction handling, as there is no additional layer between the runtime logic and the blockchain’s core.
  • Resource Management: Resource management is integral to runtime development to ensure that the blockchain operates smoothly and efficiently.
§Smart Contract Performance and Efficiency
  • Generic Nature and Overhead: Smart Contracts, particularly those running in virtual machine environments, can be less efficient due to the generic nature of their execution environment. The overhead of the virtual machine can lead to increased computational and resource costs.
  • Isolation and Security Constraints: Smart Contracts operate in an isolated environment to ensure security and prevent unwanted interactions with the blockchain’s state. This isolation, while crucial for security, can introduce additional computational overhead.
  • Gas Mechanism and Metering: The gas mechanism in Smart Contracts, used for metering computational resources, ensures that contracts don’t consume excessive resources. However, this metering itself requires computational power, adding to the overall cost of contract execution.

§Security Considerations

These two methodologies, while serving different purposes, come with their own unique security considerations.

§Runtime Security Aspects

Runtimes, being at the core of blockchain functionality, have profound implications for the security of the entire network:

  • Broad Impact: Security flaws in the runtime can compromise the entire blockchain, affecting all network participants.
  • Governance and Upgradeability: Runtime upgrades, while powerful, need rigorous governance and testing to ensure security. Improperly executed upgrades can introduce vulnerabilities or disrupt network operations.
  • Complexity and Expertise: Developing and maintaining runtime requires a higher level of expertise in blockchain architecture and security, as mistakes can be far-reaching.
§Smart Contract Security Aspects

Smart contracts, while more isolated, bring their own set of security challenges:

  • Isolated Impact: Security issues in a smart contract typically affect the contract itself and its users, rather than the whole network.
  • Contract-specific Risks: Common issues like reentrancy attacks, improper handling of external calls, and gas limit vulnerabilities are specific to smart contract development.
  • Permissionless Deployment: Since anyone can deploy a smart contract, the ecosystem is more open to potentially malicious or vulnerable code.

§Weighing and Metering

Weighing and metering are mechanisms designed to limit the resources used by external actors. However, there are fundamental differences in how these resources are handled in FRAME-based Runtimes and how they are handled in Smart Contracts, while Runtime operations are weighed, Smart Contract executions must be metered.


In FRAME-based Runtimes, operations are weighed. This means that each operation in the Runtime has a fixed upper cost, known in advance, determined through benchmarking. Weighing is practical here because:

  • Predictability: Runtime operations are part of the blockchain’s core logic, which is static until an upgrade occurs. This predictability allows for precise benchmarking.
  • Prevention of Abuse: By having a fixed upper cost that corresponds to the worst-case complexity scenario of its execution (and a mechanism to refund unused weight), it becomes infeasible for an attacker to create transactions that could unpredictably consume excessive resources.

For Smart Contracts resource consumption is metered. This is essential due to:

  • Untrusted Nature: Unlike Runtime operations, Smart Contracts can be deployed by any user, and their behavior isn’t known in advance. Metering dynamically measures resource consumption as the contract executes.
  • Safety Against Infinite Loops: Metering protects the blockchain from poorly designed contracts that might run into infinite loops, consuming an indefinite amount of resources.
§Implications for Developers and Users
  • For Runtime Developers: Understanding the cost of each operation is essential. Misjudging the weight of operations can lead to network congestion or vulnerability exploitation.
  • For Smart Contract Developers: Being mindful of the gas cost associated with contract execution is crucial. Efficiently written contracts save costs and are less likely to hit gas limits, ensuring smoother execution on the blockchain.