Web3 & DApp Development Fundamentals · Lesson

Accounts and State

EOAs and contracts.

Accounts and State is a free Web3 & DApp Development Fundamentals lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Web3 & DApp Development Fundamentals learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

What Is the World State?

Ethereum's world state is the complete snapshot of all accounts and their data at a given moment.

Every transaction transforms this state from one valid version to the next. Accounts are the building blocks of that state.

Two Types of Accounts

Ethereum has exactly two account types:

Externally Owned Accounts (EOAs) — controlled by private keys (users)
Contract Accounts — controlled by their code

Both share the same 20-byte address format.

Externally Owned Accounts

An EOA is controlled by a private key. It can initiate transactions: send ETH or call contracts.

EOAs have no code of their own — they are simply key-controlled accounts that humans (or bots) operate.

EOA {
  address: 0xAbc...123
  balance: 4.2 ETH
  nonce:   17
  code:    none
}

Contract Accounts

A contract account holds code (bytecode) and storage. It has no private key and cannot start a transaction on its own.

It only acts when called by an EOA or another contract, running its code in response.

Contract {
  address: 0xDef...456
  balance: 10 ETH
  code:    0x6080604052...
  storage: { slot0: ..., slot1: ... }
}

The Four Account Fields

Every account stores four fields:

nonce — transaction count (EOA) or contracts created (contract)
balance — ETH held, in wei
storageRoot — hash of the account's storage
codeHash — hash of the account's code

EOA vs Contract Differences

The key distinction:

Only EOAs can initiate transactions
Only contracts have code and significant storage
An EOA's codeHash is empty; a contract's is not

How State Changes

State changes only through transactions. A transaction can move ETH, deploy a contract, or call a contract that updates its storage.

After each block, the world state advances to a new, agreed-upon version.

The State Trie

All accounts are stored in a giant Merkle Patricia Trie. Its root hash — the state root — is recorded in each block header.

This single hash commits to the entire world state, just as a Merkle root commits to all transactions.

block header includes:
  stateRoot   -> all accounts
  txRoot      -> all transactions
  receiptRoot -> all receipts

Account Creation

An EOA effectively exists the moment a key pair is generated — no on-chain step is needed until it transacts.

A contract account is created when a deployment transaction runs constructor code and stores the resulting bytecode.

Smart Contract Interaction

To interact with a contract, an EOA sends a transaction specifying the contract address and the function data.

The EVM looks up the contract's code by its codeHash and executes it, possibly updating storage.

Putting It Together

Ethereum's state is a collection of accounts. EOAs are key-controlled and initiate transactions; contracts hold code and storage and react to calls.

The state root in each block commits to all of it.

Quick Check

Test your accounts knowledge.

Recap: Accounts and State

You learned that:

Ethereum has EOAs (key-controlled) and contract accounts (code-controlled)
Only EOAs can initiate transactions
Each account has a nonce, balance, storageRoot, and codeHash
The state root commits to all accounts

You have completed the Web3 fundamentals track.

Frequently asked questions

Is the “Accounts and State” lesson free?

Yes — the full text of “Accounts and State” is free to read here on the web, and the Web3 & DApp Development Fundamentals course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Web3 & DApp Development Fundamentals course, upgrade to CoddyKit PRO.

What will I learn in “Accounts and State”?

EOAs and contracts. You practise Web3 & DApp Development Fundamentals with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Web3 & DApp Development Fundamentals?

No prior experience is required. Web3 & DApp Development Fundamentals on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Accounts and State” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Web3 & DApp Development Fundamentals lesson?

Yes. Every Web3 & DApp Development Fundamentals lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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