> ## Documentation Index
> Fetch the complete documentation index at: https://docs.kronex.network/llms.txt
> Use this file to discover all available pages before exploring further.

# Smart contracts

> Deploy Solidity contracts to Kronex with Hardhat or Foundry — one endpoint, one chain ID, one compiler setting.

Kronex runs the Ethereum Virtual Machine. Solidity contracts, ABIs, events,
logs, `CREATE2`, ERC-20 and ERC-721 all behave as they do on Ethereum, and the
usual libraries — ethers, viem, web3.js — talk to a Kronex node without
modification.

There is exactly one setting you have to change, and getting it wrong produces a
contract that deploys and then reverts on every call.

## Set the EVM version to London

<Warning>
  Kronex's EVM is at **London**. Solidity 0.8.20 and newer default to
  `shanghai`, which emits the `PUSH0` opcode. `PUSH0` does not exist on Kronex,
  so a contract compiled with the default settings fails at runtime.

  Set `evmVersion` to `london` in every project.
</Warning>

What London gives you: EIP-1559 base fee and type-2 transactions, Berlin access
lists, and everything below. What it does not give you: `PUSH0`, transient
storage (`TSTORE`/`TLOAD`), and `MCOPY`.

## Hardhat

```js hardhat.config.js theme={null}
module.exports = {
  solidity: {
    version: "0.8.24",
    settings: {
      evmVersion: "london",
      optimizer: { enabled: true, runs: 200 },
    },
  },
  networks: {
    kronexTestnet: {
      url: "http://127.0.0.1:8545",
      chainId: 42069,
      accounts: [process.env.PRIVATE_KEY],
    },
  },
};
```

## Foundry

```toml foundry.toml theme={null}
[profile.default]
evm_version = "london"
optimizer = true
optimizer_runs = 200

[rpc_endpoints]
kronex_testnet = "http://127.0.0.1:8545"
```

```bash theme={null}
forge create --rpc-url kronex_testnet --private-key $PRIVATE_KEY src/Token.sol:Token
```

## Connect a library

```js theme={null}
import { JsonRpcProvider } from "ethers";

const provider = new JsonRpcProvider("http://127.0.0.1:8545", {
  chainId: 42069,
  name: "kronex-testnet",
});
```

Nothing about the provider is Kronex-specific. If your code already works
against an Ethereum node, it works here once the endpoint and chain ID point at
Kronex.

## Transactions and fees

Kronex uses EIP-1559: blocks carry a base fee, and the priority fee is what
miners compete for. Type-0 (legacy), type-1 (access list) and type-2 (dynamic
fee) transactions are all accepted, and `eth_feeHistory`,
`eth_maxPriorityFeePerGas` and `eth_estimateGas` work as usual.

<Note>
  The priority fees a block collects are not paid entirely to the block's
  sealer. They are pooled and split across the block's recipients — see
  [Rewards](/learn/rewards). This changes nothing for the sender.
</Note>

## Chain-specific data

Anything Kronex adds on top of Ethereum lives in the `krnx_` namespace: supply,
lockups, reward schedules, mining status. See the
[RPC reference](/rpc/overview).