Once a smart contract is deployed on the Ethereum blockchain, its code becomes immutable, meaning developers cannot make modifications or fix bugs without redeploying. To address this challenge, Ethereum has testnet RPC nodes — where developers can connect to safely test and debug smart contracts before launching on the mainnet.

In this guide, we explore the Sepolia testnet—what it is, how it works, and how to connect to it.

What is Sepolia?

Sepolia is a test network for Ethereum launched in 2021 that operates independently of the main network (mainnet) but closely simulates its conditions.

Key features:

• Ease of access

• Free to use

• Serves to run realistic tests

It provides decentralized application and developer tooling builders with an environment for testing their solutions before moving to the Ethereum mainnet.

How Ethereum Sepolia works

The test network mirrors the mainnet’s functionality, including transaction processing, block production, and smart contract deployment.

1. It lets developers see how their code will behave in a live environment: estimate gas usage, deployment costs, test how applications interact with other services, and process different transaction types.

2. The testnet has its own block explorers that allow users to view on-chain data specific to Sepolia.

3. It used to test protocol upgrades and hard forks (like upcoming Pectra) before they go live on mainnet so developers can test how these changes affect dApps and smart contracts.

4. Supported by popular Ethereum development frameworks and tools like Remix, Hardhat, and Foundry, it makes the transition from testing to development easy.

Developers can interact with Sepolia using testnet Ethereum RPC (Remote Procedure Call) endpoints, similar to how they would on the mainnet.

What is Sepolia ETH?

Sepolia uses test Ether (ETH) which serves the same purpose as ETH on the mainnet but has no actual value. Developers can request test ETH from faucets that provide them for free.

These tokens allow developers to interact with the network as they would on the mainnet—sending transactions, paying for gas fees, deploying contracts, and more.

Ethereum Layer 2 Sepolia networks

Layer-2 (L2) networks work on top of Ethereum and have their own test networks linked to Ethereum's Sepolia testnet.

• Base Sepolia

• Arbitrum Sepolia

• Optimism Sepolia

• Scroll Sepolia

By using these Sepolia-based testnets, developers can simulate interactions between Ethereum's main network (Layer 1) and L2 chains, which closely replicate real-world conditions.

Sepolia vs other Ethereum Testnets

Every few years, Ethereum introduces a new ‘sandbox’ network to keep the testing environment fresh and stable, preventing performance issues over time.

With the recent deprecation of Goerli, Ethereum now maintains two primary testnets: Sepolia and Holesky. Let’s compare the three.

Sepolia vs Holesky

Introduced in 2023, Holesky replaced Goerli as the primary testnet for staking tests. It operates on Proof of Stake (PoS) meaning that anyone without restriction can become a validator by staking test tokens, similar to how Ethereum’s mainnet works.

Sepolia, on the other hand, is optimized for application testing. It is secured by a closed validator set, where a few trusted validators are responsible for processing transactions. This is done to provide a stable and controlled environment for testing.

Sepolia vs Goerli

Before Sepolia, Goerli was the go-to testnet for Ethereum developers to deploy and test applications, as it allowed full testing of both its consensus and execution layers. However, in January 2024, Goerli was deprecated and is no longer in sync with the Ethereum ecosystem.

Sepolia has become the default testnet for Ethereum developers. It provides a near-mainnet testing environment without the issues Goerli faced, such as excessive historical records, high resource demands, and speculative trading of Goerli ETH.

In other words, developers rely on Sepolia as Ethereum's primary testnet.

Why use Sepolia?

Here’s why developers choose Sepolia:

• Active maintenance: Supported long-term by the community, Sepolia provides a stable, reliable environment that evolves alongside Ethereum protocol updates.

• Long-term support: Sepolia is here to stay at least till 2026, allowing developers to run tests on applications over an extended period.

• Accessible test ETH: Sepolia ETH is abundantly available through faucets, which distribute tokens for free and prevent the speculative problems.

With that, Sepolia offers a reliable, low-risk environment for testing blockchain-based applications and interactions.

How to connect to Sepolia testnet

To connect to Sepolia and start using it, follow these two steps:

• Retrieve a Sepolia network node RPC URL

• Fund the wallet with test tokens

GetBlock, a blockchain infrastructure service, simplifies the process by providing the necessary resources and tools.

Image: GetBlock, MetaMask

Here’s how to connect MetaMask to Ethereum Sepolia testnet using GetBlock’s free endpoints and a faucet:

1. Sign up on GetBlock to generate your personal JSON-RPC URL for Sepolia.

2. Manually add Sepolia to MetaMask by adding the correct network parameters.

3. Use GetBlock’s testnet faucet to get 0.1 SepoliaETH to start using the added network.

Follow these same steps to connect to Layer 2 Sepolia testnets, if needed.

Conclusion

In short, Sepolia is a must have tool for developers who want to make sure their smart contracts are reliable and efficient before deploying to the Ethereum mainnet. For blockchain users, especially, beginners, it gives an opportunity to interact with blockchain before risking real money.