Goerli and Sepolia are two testnets that Ethereum developers use to test their applications. There are multiple reasons web3 developers should consider before choosing a testnet including availability of test ETH, RPC node provider support, smart contract availability, and more. 

In this article we will cover what each testnet is, their technical differences, highlight three considerations, and help you choose the best Ethereum testnet for your project.

Deprecation Notice

While you can use the Goerli testnet, we caution against it as the Ethereum Foundation has announced that Goerli will soon be deprecated. Therefore, we recommend using Sepolia testnet as Alchemy has full Sepolia support and a free Sepolia faucet.

What is the Goerli testnet?

Goerli started off as a hackathon project at ETH-Berlin in 2018 before being officially launched in 2019. The Goerli test network is a public, Proof-of-Stake (PoS) testnet that is maintained with an open validator set, meaning anyone who wishes to run their own testnet validator can participate. However, due to the large state of the network, it requires a longer time to sync and more storage to run a node. 

Key Differences Compared to Sepolia

• Open validator set
• Access to consensus is permissionless
• Supports cross client functionality
• Carries a large state and requires high storage commitments
• Requires a longer time to synchronize with the present state of the network

Goerli Chain Information

If you are adding the Goerli blockchain to your wallet, this is the Goerli chain ID and network information to include:

• Network Name - Goerli Test Network
• RPC URL - https://eth-goerli.g.alchemy.com/v2/[YOUR-API-KEY]
• Chain ID - 5
• Currency Symbol - GoerliETH
• Block explorer URL - https://goerli.etherscan.io/

To start building on Goerli, sign up for a free Alchemy account, and get free GoerliETH tokens from Alchemy's public Goerli faucet.

What is the Sepolia testnet?

Launched in 2021, Sepolia is a permissioned Proof-of-Stake test network maintained by a closed validator set primarily controlled by client and testing teams. While developers can use the testnet publicly to test and deploy their decentralized applications (dapps), not everyone can opt to run a validator node, making it a permissioned network

Since Sepolia, being a younger testnet, has fewer deployed applications as compared to more mature testnets like Goerli. It has a smaller state and history, allowing for faster syncing and requiring minimal disk space to run a node.

Key Differences Compared to Goerli

• Closed validator set (Proof-of-Authority configuration)
• Access to consensus is permissioned
• The validator set is restricted and mainly overseen by client and testing teams
• Supports cross-client compatibility
• Smaller blockchain state and history
• Fast to sync and requires fewer storage commitments

Sepolia Chain Information

If you are adding the Sepolia blockchain to your wallet, this is the Sepolia chain ID and network information to include:

• Network Name - Sepolia Test Netwok
• RPC URL - https://eth-sepolia.g.alchemy.com/v2/[YOUR-API-KEY]
• Chain ID - 11155111
• Currency Symbol - SepoliaETH
• Block Explorer URL - https://sepolia.etherscan.io/

To start building on Sepolia, sign up for a free Alchemy account, and get free SepoliaETH tokens from Alchemy's public faucet.

Things to Consider Before Choosing to Develop on Sepolia or Goerli

The three things to consider before selecting either the Sepolia test network or Goerli are: the availability and cost of test ETH, RPC and API support, and smart contract availability.

1. Availability of Test ETH

The main consideration when choosing between Goerli and Sepolia is the availability, accessibility, and cost of acquiring test ETH tokens. Test ETH tokens are used to pay for gas on testnets, and are required by web3 developers to deploy and test their smart contracts in an environment that closely mirrors the Ethereum mainnet environment.

Is Goerli ETH free?

Historically, the test ETH that developers use on the Goerli testnet, goETH, has been free, however because of the scarcity of goETH, liquid markets have been created where developers can buy and sell goETH for real ETH.

Web3 developers can still access free Goerli ETH through a Goerli Faucet, but because of a hard cap on the total amount of goETH, there is a limit to how much goETH can be received each day.

The scarcity and cost associated with accumulating Goerli ETH is one reason why many Ethereum developers are switching from Goerli to Sepolia.

Is Sepolia ETH free?

Yes, Sepolia ETH is free, and can be received from a Sepolia ETH faucet. Because there is no cap on the total number of sepETH available in the market, faucet providers like Alchemy are able to provide developers with larger amounts of sepETH each time they request test ETH from a Sepolia faucet.

2. RPC and API Support

Before deciding to build on Sepolia or Goerli, it’s important to understand the RPC node providers that support each testnet, and the API endpoints that they support. For example, some RPC providers like Alchemy support the Sepolia testnet, while other providers may not. Additionally, some RPC providers may lack support for important API endpoints, such as trace APIs which require Erigon nodes.

Alchemy supports all the core JSON-RPC methods on Sepolia as well as archive node support and trace API endpoints. Alchemy will also support enhanced API methods on Sepolia in the future.

3. Smart Contract Availability

If your smart contracts rely on other smart contracts, your decision to build on Goerli vs. Sepolia will be determined by where the dependent smart contracts are deployed.

For example, if your smart contracts need to access the Uniswap v3 contracts, and Uniswap has only deployed their contracts on the Goerli testnet, then you will need to deploy your smart contracts on Goerli until Uniswap migrates their testnets to Sepolia.

4. Additional Considerations

Besides smart contract availability and support from node providers, factors such as network stability, validator set, and long-term-support by the Ethereum Foundation should be considered when choosing between Goerli and Sepolia test networks.

Goerli or Sepolia: Which testnet should I choose?

Choosing the right test network is an important decision that can impact the success of your dapp development. Each test network has its own technical specifications, features, and tradeoffs where selecting the right one can save you time and resources.

When it comes to deploying and testing applications and smart contracts, Ethereum.org recommends Sepolia as the primary choice for testing applications and smart contracts due to its restricted validator set and higher stability guarantees.

On the other hand, if you're looking to test your beacon chain validators, node setups, client versions, or want to try out protocol upgrades before deploying to the main network, Goerli is a good option. It's the closest testnet to the Ethereum mainnet and can also be useful for testing complex smart contract interactions.