# zkApps for Ethereum Developers

> How zkApps and Ethereum smart contracts compare, differences in language, execution environment, transaction costs, application storage, developer tooling, scaling, and consensus.

Canonical URL: https://docs.minaprotocol.com/zkapps/advanced/zkapps-for-ethereum-developers

Mina and Ethereum are both decentralized, programmable, layer-one blockchains,
but they are designed in fundamentally different ways. The Ethereum network
verifies transaction execution by having every node execute every transaction.
While this design solves a real problem, it also imposes some severe limitations
on privacy and scalability.

The Mina Protocol works differently. It verifies transactions (and previous
blocks) cryptographically using recursive zero knowledge proofs. Smart contract
code is written in TypeScript and executes off chain. Mina nodes need to
verify only a small proof in order to validate the associated execution. Better
still, the proof does not reveal any information about the underlying
computation, meaning developers can choose whether their inputs and outputs
should be public or private, depending on the requirements of their application.

## At a Glance

<table style={{borderSpacing: '0px'}}>
<thead>
  <tr>
    <th style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}></th>
    <th style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px', fontSize: 'larger'}}>Ethereum Smart Contracts</th>
    <th style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px', fontSize: 'larger'}}>Mina zkApps</th>
  </tr>
</thead>
<tbody>
  <tr>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px', fontSize: 'larger'}}>Language</td>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}>Smart contracts are written in <span style={{color: '#7d4bbd'}}>Solidity</span>.</td>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}>zkApp smart contracts are written using <span style={{color: '#7d4bbd'}}>o1js</span> (a <span style={{color: '#7d4bbd'}}>TypeScript</span> library).</td>
  </tr>
  <tr>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px', fontSize: 'larger'}}>Execution Environment</td>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}>Smart contracts run on <span style={{color: '#7d4bbd'}}>every Ethereum node</span>.</td>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}>zkApps run <span style={{color: '#7d4bbd'}}>client side</span> in a user’s web browser, and publish only a small validity proof which is verified by the Mina nodes.</td>
  </tr>
  <tr>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px', fontSize: 'larger'}}>Transaction Cost</td>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}>Execution costs are variable, and determined using a <span style={{color: '#7d4bbd'}}>gas model</span>.</td>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}>Execution costs are <span style={{color: '#7d4bbd'}}>small</span>, and <span style={{color: '#7d4bbd'}}>constant</span> because the Mina nodes are verifying the same size proof regardless of the amount of client-side computation.</td>
  </tr>
  <tr>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px', fontSize: 'larger'}}>Application Storage</td>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}>Ethereum is designed around the idea that storage, and computation are inherently coupled; <span style={{color: '#7d4bbd'}}>all state must live on every Ethereum node</span>.</td>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}>Mina’s design allows state, and computation to be decoupled so that <span style={{color: '#7d4bbd'}}>application state can live anywhere</span>; developers can choose a solution that fits their cost/security requirements best.</td>
  </tr>
  <tr>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px', fontSize: 'larger'}}>Developer Tooling</td>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}>New developer tools with unusual patterns like <span style={{color: '#7d4bbd'}}>Hardhat</span>, and <span style={{color: '#7d4bbd'}}>Truffle</span> are needed in order to manage the deployment of Ethereum smart contracts.</td>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}><span style={{color: '#7d4bbd'}}>The zkApp CLI</span> manages scaffolding, linting, testing, and deployment using common JavaScript/TypeScript tools you are already familiar with.</td>
  </tr>
  <tr>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px', fontSize: 'larger'}}>Scaling</td>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}>Ethereum nodes must execute every transaction directly making <span style={{color: '#7d4bbd'}}>horizontal scaling hard</span>.</td>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}>Mina’s recursive zero knowledge proofs allow snark-workers to compress the blockchain, and developers to compress transactions using <span style={{color: '#7d4bbd'}}>native rollups</span> for <span style={{color: '#7d4bbd'}}>exponential scaling</span>.</td>
  </tr>
  <tr>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px', fontSize: 'larger'}}>Consensus</td>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}>Ethereum nodes must download the entire block history (<span style={{color: '#7d4bbd'}}>~700GB</span>) in order to verify the current finalized chain state.</td>
    <td style={{borderColor: 'black', borderWidth: '1px', borderStyle: 'solid', padding: '10px'}}>Mina clients can verify the current finalized state using a single <span style={{color: '#7d4bbd'}}>22KB</span> recursive zero knowledge proof.</td>
  </tr>
</tbody>
</table>

## Example Code

```ts


export class Add extends SmartContract {
  /* The state decorator tells o1js to store/retrieve num from the Mina
  blockchain */
  /* The Field type represents elements of a finite field (similar to uint256
  for practical purposes, but loops back to 1 after overflowing) */
  @state(Field) num = State<Field>();

  // Initialize the contract (similar to a constructor in Solidity)
  init() {
    super.init();
    // Set num equal to a Field element of value 1 on contract deployment
    this.num.set(Field(1));
  }

  /* The method decorator tells o1js to be ready to generate a proof of
  execution any time this method is called */
  @method async update() {
    // Get the state of num from the Mina blockchain and set it to currentState
    const currentState = this.num.get();
    /* Calling add instead of using the JS infix addition operator enables
    o1js to prove that the addition is done correctly */
    const newState = currentState.add(2);
    /* Set the state of num on the Mina blockchain equal to newState (this
    state update will not happen unless the transaction is accompanied by
    a valid proof of execution) */
    this.num.set(newState);
  }
}
```

## How does Mina bridge to Ethereum?

Mina proofs are small and easy to verify; this means that any Turing complete
blockchain (like Ethereum) can validate the entire Mina state in a single
transaction using a bridge contract. These are a bit different from existing
bridging solutions because they don't require additional security
assumptions. Think of them as full Mina nodes that are implemented in smart
contracts on other chains. They validate the Mina state in exactly the same way
a Mina block producer would and expose Mina directly to any other contract.
The Nil Foundation is working on the [first of these bridges](https://verify.mina.nil.foundation/walkthrough/index.html) for Ethereum and other EVM-compatible networks.

### Have another question?

Reach out in the [#zkapps-developers](https://discord.com/channels/484437221055922177/915745847692636181) channel on Mina Protocol Discord. It's better when we learn together.