Smart Contracts: When Code Executes the Rules

Blockchain does not have to serve only as a way to transfer cryptocurrencies. It can also store and execute pre-programmed rules. This is exactly the principle behind smart contracts – programs stored on the blockchain that automatically perform a certain action once defined conditions are met. They can, for example, transfer a token, exchange digital assets, manage collateral on a loan, or issue an NFT.

What is a smart contract

The name can be a bit misleading. A smart contract is not necessarily a contract in the legal sense, and it is not "smart" in the way artificial intelligence is. It is simply a program that contains predefined rules and performs certain operations according to them.

Its logic can be summed up simply: if condition A occurs, perform action B. A smart contract therefore does not make decisions and does not try to understand the user's intent. It only executes what it has been programmed to do.

A smart contract as a vending machine

A good analogy is a vending machine. We insert the correct amount, select a product, and the machine dispenses it. If the conditions are not met, nothing happens.

A smart contract works similarly. Instead of a physical machine, it is a program on the blockchain, and the result can be, for example, a cryptocurrency transfer, the issuance of a token, or the execution of a financial operation.

A smart contract does not decide. It executes.

Why smart contracts came into existence

When two people who don't know each other trade with one another, a trust problem arises: who should fulfill their side of the deal first?

In the traditional system, this role is often handled by banks, exchanges, custodians, or payment companies. A smart contract makes it possible to shift part of this role into a program.

For example, when exchanging a digital asset, the buyer can deposit funds into a smart contract and the seller can deposit the requested asset. If both conditions are met, the contract automatically settles both sides of the transaction.

Ethereum and the programmable blockchain

Bitcoin supports a certain amount of programmable logic, but its main function remains the transfer and storage of digital value. Ethereum expanded on this idea and made it possible to run more general programs on the blockchain.

This is precisely what gave rise to a large part of today's world of decentralized applications. Smart contracts are behind, for example, decentralized exchanges, DeFi, stablecoins, NFTs, or tokenized assets.

Using smart contracts costs something

Every operation on the blockchain requires computing resources. On Ethereum, the cost of this work is referred to as gas.

The more complex the operation a smart contract performs, the higher the fee can be. This is one reason Layer 2 networks have emerged, allowing many transactions to be processed more efficiently and cheaply.

What smart contracts made possible

Smart contracts are the foundation of a whole range of blockchain applications. On decentralized exchanges, they can manage token swaps and liquidity. In DeFi, they are used, for example, for loans, collateral, or reward payouts.

For stablecoins, they can manage issuance, transfers, or collateral management. For NFTs, they determine, for example, ownership and transfer rules. They also play an important role in asset tokenization, where a blockchain token can, under certain conditions, represent a specific economic right or a stake in another asset.

Smart contracts as digital LEGO

Individual smart contracts can work together. This principle is referred to as composability.

They can be thought of as digital LEGO. One contract might manage a stablecoin, another a decentralized exchange, and another loans or price data. A developer can then use already existing contracts as building blocks for a new application.

The advantage of interconnection is also a risk. If one application depends on several other contracts, a problem in one of them can spread further.

A smart contract cannot see into the real world

A smart contract works well with information stored on the blockchain. On its own, however, it does not know, for example, the current price of gold, the EUR/USD exchange rate, the result of a sports match, or whether a shipment has been delivered.

If it needs information from the outside world, it uses what are known as oracles. These serve as a bridge between the blockchain and external data.

This, however, creates another risk. If an oracle provides incorrect data, a smart contract may correctly execute the wrong action. The security of the system therefore depends not only on its code, but also on the quality of the data it uses.

Code does exactly what is written

Predictability is one of the main advantages of smart contracts, but at the same time also one of their weaknesses. The program does not know what the developer intended. It only executes what was actually programmed.

A well-known example is the The DAO project from 2016, when a bug in a smart contract was exploited to drain approximately 3.6 million ETH. This case showed that a blockchain can correctly execute rules, but if the bug already lies in the program itself, decentralization does not automatically fix it.

A decentralized blockchain does not automatically mean a decentralized application

A smart contract can run on a decentralized blockchain, but the application built around it can still contain centralized elements. Some contracts can be updated, paused, or managed through administrator keys or a multisig.

Simply knowing that a service uses blockchain is therefore not enough. It is more important to find out who can change its rules and which parts of the system still require trust in specific individuals or infrastructure.

Advantages and risks of smart contracts

Key advantages include automation, transparency, programmability, composability, and global accessibility. Smart contracts make it possible to build applications whose rules can be executed automatically without manual intervention.

On the other hand, there are risks such as bugs in the code, incorrect data from an oracle, administrator privileges, dependency on other contracts, or the underlying blockchain network itself. User behavior can also be a risk, for example confirming a malicious transaction or using a fraudulent application.

What to check before use

The average user does not need to be able to read programming code. They should, however, care about who created the application, how long it has been running, whether its contracts have been audited, whether they can be updated, and who has administrative control over the system.

The more complex an application is, the more important it is to understand that its security does not depend on a single smart contract alone, but on the entire architecture surrounding it.

Conclusion

At its core, a smart contract is a simple concept: a program on the blockchain receives a certain input, checks predefined rules, and carries out a specific action. Thanks to this, blockchain has expanded from a simple transfer of cryptocurrencies to financial applications, digital assets, and automated processes.

Smart contracts, however, do not eliminate trust or risk entirely. Trust merely shifts – from intermediaries toward the code, the data, and the people who can control or change the system.

It is therefore not enough to know that an application "uses smart contracts." What matters is understanding what the contract actually does, where it gets its information from, who has control over it, and what it depends on.

This text is intended for informational and educational purposes only and does not constitute investment advice. Crypto assets are volatile, and you may lose the entire amount invested.