# Develop Smart Contracts and Dapps

## Overview

Considering that Cronos zkEVM is based on zkSync technology, the zkSync docs at <https://docs.zksync.io/> apply to Cronos zkEVM as well.

## Cronos zkEVM Mainnet&#x20;

As far as the Cronos zkEVM testnet is concerned, the main differences with zkSync Era are:

* The JSON RPC URL: <https://mainnet.zkevm.cronos.org>
* The Chain ID: `388`
* The blockchain explorer URL: <https://explorer.zkevm.cronos.org/>
* WebSocket (rate limited): `wss://ws.zkevm.cronos.org`

{% hint style="info" %}
Please expect the JSON-RPC and WebSocket URLs to be rate limited. Rate limits will change over time.
{% endhint %}

* The denomination of the L2 protocol token: zkCRO
* Gas price: :warning: The gas price of is currently fixed at `1250gwei`
  * This is subject to change and is expected to be dynamic in the next major release to be announced.

{% hint style="warning" %}
Whereas zkSync Era uses ETH as the token to pay for transaction fees on the Layer 2, Cronos zkEVM uses zkCRO. This means that the gas token of Cronos zkEVM (zkCRO) is different from the gas token on the Layer 1 (Ethereum). This is a major difference that developers need to take into account when they create cross-chain transactions.
{% endhint %}

***

## Cronos zkEVM Sepolia Testnet&#x20;

As far as the Cronos zkEVM Sepolia testnet is concerned, the main differences with zkSync Era are:

* The JSON RPC URL: <https://testnet.zkevm.cronos.org>
* The Chain ID: `240`
* The blockchain explorer URL: <https://explorer.zkevm.cronos.org/testnet/>
* WebSocket (rate limited): `wss://ws.testnet.zkevm.cronos.org`

{% hint style="info" %}
Please expect the JSON-RPC and WebSocket URLs to be rate limited. Rate limits will change over time
{% endhint %}

* Gas price: :warning: The gas price of is currently fixed at `1250gwei`
  * This is subject to change and is expected to be dynamic in the next major release to be announced.
* The denomination of the L2 protocol token: zkTCRO


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