What are testnets?

As more funds and users are onboarded to Web3 and decentralized finance (DeFi) services, security and reliability are becoming increasingly important for developers. Testnets are used by developers to ensure that the smart contracts and apps they deploy are functional and secure.

Developers can work with the same clients as they would on the mainnet, but testnets operate on a separate ledger. This separation creates a low-risk environment where developers can test and experiment without the costs of deploying on the mainnet.

What are testnets?

Testnets are test blockchain networks that act and perform similarly to the main networks (mainnets) they are associated with. Since they operate on separate ledgers from the mainnet, the coins on a testnet have no connection to transactions and value on the mainnet. This allows developers to deploy, test, and execute their projects on a functioning blockchain freely.

The cost of failure or mistakes on a mainnet is very high and at times irreversible, so developers need an environment where they can comfortably work without these risks.

Security is a high priority for developers working on any decentralized platform. Operating on a testnet also offers the benefit of investigating vulnerabilities and educating developers on how the platform works. For testnets that precede network upgrades, it is important to investigate how newly developed changes function before they are merged with the mainnet.

Differences between mainnets and testnets

Most testnets have separate wallet systems to make it easier to manage coins and transactions outside of the mainnet. When deploying contracts and using services like Alchemy, testnets have distinct Network IDs.

For example, on the Ethereum network:

• Ethereum mainnet — 1
• Sepolia testnet — 11155111

Older Ethereum testnets such as Ropsten, Rinkeby, Kovan, and Goerli have been deprecated. Do not use them for new development.

These IDs are used to ensure that the contract is deployed to the correct network and that the correct wallet system is used. Testnets do not experience the same amount of transaction frequency compared to their mainnets.

Ethereum testnets

Alchemy recommends Sepolia as the Ethereum testnet for application developers. Alchemy has full Sepolia support and a free Sepolia faucet.

Sepolia is a proof-of-stake testnet maintained by Ethereum core developers. It was designed to simulate harsh network conditions and has shorter block times, which enable faster transaction confirmation and feedback for developers. Sepolia's testnet token supply is uncapped, so developers are less likely to face the token scarcity that made earlier testnets unusable.

Transactions can be viewed on Etherscan. For Base, Alchemy also covers how to get Base Sepolia ETH.

Want to start building on Ethereum testnets? Create a free Alchemy developer account to start building.

Frequently asked questions

What are testnets?

Testnets are test blockchain networks that act and perform similarly to mainnets but operate on separate ledgers, allowing developers to deploy, test, and execute projects without the risks and costs of using the mainnet.

What is the difference between a Testnet and a Mainnet?

Testnets operate on separate ledgers from mainnets, use simulated tokens with no real value, and allow developers to test safely, while mainnets handle live transactions with actual cryptocurrency assets.

Are Testnet tokens worth anything?

No, testnet tokens have no connection to transactions and value on the mainnet and hold no real-world monetary value.

Why do developers use testnets?

Developers use testnets to ensure their smart contracts and apps are functional and secure before deploying to mainnet, creating a low-risk environment for testing and experimentation.

Which Ethereum Testnet should I use?

Use Sepolia. Earlier Ethereum testnets including Ropsten, Kovan, Rinkeby, and Goerli have been deprecated.

What makes Sepolia different from other testnets?

Sepolia has shorter block times for faster transaction confirmation, simulates harsh network conditions, and has an uncapped number of testnet tokens, making it less likely for developers to face token scarcity.

How do testnets improve blockchain security?

Testnets allow developers to investigate vulnerabilities, test network upgrades, and identify issues before deploying to mainnet, where the cost of failure would be very high and potentially irreversible.

Can anyone access testnets?

Yes, testnets are accessible to developers who need to test their applications, and services like Alchemy provide free faucets to obtain testnet tokens for experimentation.