Interactive guide · Live data

Smart contracts
agreements that code themselves

Digital contracts that execute automatically when conditions are met — no lawyers, no middlemen, no waiting. Here is how they work and why they matter.

Self-executing Tamper-proof Programmable money

Total market cap

$2,28 T

▼ -0,95 % / 24h

Live

Volume 24h

$52 206 111 113

BTC Market dominance

56,5%

ETH Market dominance

10,0%

active cryptocurrencies

18 374

Start the guide

Part 1 · The basics

What is a smart contract?

A smart contract is a program stored on a blockchain that runs automatically when its predefined conditions are met. Think of a vending machine: put in a coin, get a product — no human in the middle.

Once deployed, the code cannot be changed, and the outcome is the same for everyone. That is why smart contracts can replace intermediaries for many agreements.

1 Automatic

Execution is triggered by events, on-chain data or time — no human action needed.

2 Transparent

The code and its state are public on-chain and auditable by anyone.

3 Unstoppable

No single party can censor, pause or alter a contract once it is live.

Where they run : Most smart contracts run on Ethereum, written in Solidity and executed by the Ethereum Virtual Machine (EVM). Other chains (Solana, Cardano, Avalanche) have their own variants.

Part 2 · How it works

Anatomy of a smart contract

From code to on-chain execution, here is the lifecycle of a smart contract.

1

Writing

A developer writes the logic in a language like Solidity, defining rules, variables and conditions.
2

Deployment

The compiled bytecode is deployed to the blockchain via a transaction, which costs gas and is paid in ETH.
3

Triggering

Users interact by sending transactions or when an oracle feeds real-world data (prices, events) into the contract.
4

Execution

The EVM executes the code deterministically on every node. The result is identical for everyone.
5

State change

The outcome — a transfer, an NFT mint, a payout — is recorded on-chain, permanently and publicly.

Part 5 · The models

Smart contract vs traditional contract

Compare the two approaches: who enforces, who verifies, and what it costs.

PoW

Security 95/100

Decentralization 90/100

Energy 15/100

Speed 20/100

PoS

Security 88/100

Decentralization 75/100

Energy 95/100

Speed 60/100

DPoS

Security 70/100

Decentralization 45/100

Energy 98/100

Speed 95/100

Part 6 · The sentiment

Fear & Greed index

The Fear & Greed index (0 = extreme fear, 100 = extreme greed) measures crypto investor sentiment. Current value:

Fear

30-day history

Part 7 · The data

Live market

Top cryptocurrencies and their 24h change. Data refreshed every 3 minutes (CoinGecko).

#	Coin	Price	24h	Mkt cap	Volume 24h
1	Bitcoin BTC	$64 327	-1,20 %	$1,29 T	$21,19 Md
2	Ethereum ETH	$1 892	-1,70 %	$228,28 Md	$7,46 Md
3	Tether USDT	$1,00	+0,00 %	$183,10 Md	$34,82 Md
4	BNB BNB	$607,47	+0,50 %	$80,88 Md	$618,4 M
5	USDC USDC	$1,00	+0,00 %	$72,10 Md	$8,25 Md
6	XRP XRP	$1,01	-2,50 %	$63,00 Md	$1,09 Md
7	Solana SOL	$76,16	-0,90 %	$44,36 Md	$1,39 Md
8	TRON TRX	$0,34	+1,70 %	$31,91 Md	$460,3 M

Crypto converter →

Convert 20+ cryptocurrencies to 30 world currencies with live prices.

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SHA-256 generator →

Generate SHA-256 hashes instantly — a must-have for developers.

Mining cost calculator →

Estimate mining profitability and energy cost.

Part 8 · The ecosystem

How they are used

Smart contracts power the entire Web3 economy. A few of the biggest applications.

Token contracts

ERC-20 & ERC-721
Mint, transfer, burn
Powers DeFi & NFTs
Audited & battle-tested
Own the standard

Automated payments

Escrow & payroll
Release funds on condition
No trust required
Programmable streams
Instant settlement

Governance

DAO voting
Proposals on-chain
Transparent treasury
Token-weighted votes
Community-driven

Part 9 · The applications

Real-world use cases

Beyond crypto, smart contracts automate agreements everywhere trust costs money.

DeFi lending

Automatic interest, liquidations and loans with zero paperwork.

NFT royalties

Creators automatically earn a percentage on every resale, forever.

Supply chain

Payments released automatically when goods pass customs or are delivered.

Insurance

Flight-delay policies that pay out instantly from oracle data.

Escrow

Buyers and sellers trade without trusting each other: funds unlock on delivery.

Charity & aid

Donations tracked end-to-end, released only when milestones are met.

Part 10 · The verdict

Advantages & Limitations

Advantages

✔Automation removes middlemen, delays and manual errors.
✔Trustless: code enforces the agreement, not a counterparty.
✔Transparent and auditable by anyone.
✔Programmable: composable with other contracts (DeFi Lego).
✔Runs 24/7 without downtime or jurisdiction limits.

Limitations

✕Bugs in code can be exploited (audits are essential).
✕Once deployed, contracts are hard to change.
✕Oracles can be manipulated or fail.
✕Legal status is unclear in most jurisdictions.
✕High development and gas costs on Ethereum.

Part 11 · The vocabulary

Quick glossary

The smart-contract terms you need to know.

Solidity

The main programming language for Ethereum smart contracts.

EVM

Ethereum Virtual Machine — the runtime that executes contract bytecode.

Gas

The fee, paid in ETH, to execute operations on the blockchain.

Deploy

Publishing a contract to the blockchain so it becomes live and immutable.

Immutable

Cannot be changed after deployment — a core property of deployed contracts.

Oracle

A service that brings off-chain data (prices, weather, events) into a contract.

Audit

A security review of contract code to find bugs before launch.

DApp

A decentralized application that uses one or more smart contracts.

ABI

Application Binary Interface — how applications call contract functions.

Revert

Undoing all state changes of a transaction when execution fails.

Access control

Rules limiting who can call sensitive contract functions.

Upgradeable

A design pattern allowing contract logic to be updated via proxies.

Part 12 · Questions

Smart contract FAQ

What is a smart contract in simple words?

A smart contract is a computer program stored on a blockchain that runs automatically when conditions are met. It is like a vending machine for agreements: no human needed to enforce the deal.

Are smart contracts legal?

It depends on the jurisdiction. Some countries recognize them, others do not yet. Even where their legal status is unclear, they are binding in practice because the code executes and settles value automatically.

How much does it cost to deploy a smart contract?

Deployment costs gas, which varies with Ethereum congestion. A simple contract may cost $10–100; complex ones can cost several hundred dollars. Layer-2s are far cheaper.

Can a smart contract be hacked?

Yes, if the code has vulnerabilities. That is why professional audits and bug bounties are standard. The blockchain executes the code faithfully; the risk is in the code itself.

What language are smart contracts written in?

Mostly Solidity on Ethereum, but also Vyper, Rust (Solana), and Cairo (Starknet). The language depends on the blockchain.

Who runs the smart contract?

Every node in the network executes it as part of transaction processing. That decentralization is what makes it tamper-proof.

What is an immutable smart contract?

An immutable contract cannot be changed after deployment. This guarantees predictable behavior but means bugs cannot be patched; developers use upgradeable patterns when updates may be needed.

Are smart contracts expensive to run?

Execution costs gas, which depends on network load and complexity. Simple transfers are cheap; complex logic costs more. Layer-2 rollups reduce costs dramatically.

This page is for education only and does not constitute legal or financial advice.

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Quick links

Part 1 · The basics Part 2 · How it works The chain of blocks, live Hashing & immutability Proof of work Consensus comparison Fear & Greed index

Smart contracts agreements that code themselves