What is the difference between a mainnet and a testnet?

Testnets play an important role in the development and maintenance of blockchains and decentralized applications. Built to be accurate replicas of the primary mainnets they are paired with, testnets allow for the testing and evaluation of blockchain upgrades and improvements without impacting the stability or security of a live network.

In this AAG Academy guide, we’ll explain what testnet blockchains are and how they work, look at some examples of the biggest testnets in use today, and cover how a testnet differs from a mainnet. We’ll also answer some commonly asked questions.

What is a testnet?

A testnet is a special type of blockchain that allows developers to test out new features and improvements before they are deployed to the main network, or mainnet. Making changes of any kind to a live blockchain is an incredibly risky process. If anything goes wrong, it can lead to outages, or in the worst case scenario, vulnerabilities that could be exploited by attackers.

With that being the case, live blockchains, especially larger ones, are very rarely tweaked or upgraded before any planned changes are stringently tested. This involves first making the changes on a testnet and then scrutinizing them under a wide range of scenarios to ensure that they are as solid as they can be — and that no inadvertent issues are introduced.

Testnets may also be utilized by developers of decentralized applications (DApps), who need to test and evaluate upcoming releases or updates before they are released to the public. The process for this is somewhat similar; the application is deployed on the testnet and subjected to a variety of checks to ensure that it is stable, works as intended, and is free from obvious flaws.

In some cases, developers may invite users to try the testnet so that they can look for errors under close-to-real-world scenarios. They may also ask for feedback on the changes they are planning to introduce. Assuming there are no problems after these processes are carried out, the upgrades and improvements can then be made to the live mainnet.

How does a testnet work?

A testnet is most effective when it can deliver an accurate real-world experience, so most are an exact copy of their original blockchain. They use the same underlying code and operate in the same way. To achieve this, developers create replicas of the mainnet’s “genesis blocks” — the very first blocks that were added to the blockchain.

It’s important to note that although testnets are identical to their original blockchain, they are entirely separate. Any changes made to them, or any actions performed on them, do not impact the primary blockchain in any way. This also means that any coins or tokens created on the testnet cannot be transferred to the mainnet, and vice-versa.

One of the very first testnets was launched in late 2010 after Bitcoin developer Gavin Andresen submitted a request for a separate blockchain, identical to the original, that would allow for experimentation without impacting the primary Bitcoin blockchain. Later upgrades to this testnet fixed early teething problems, like increased mining difficulty and BTC coin fraud.

For certain decentralized projects, potential changes may be subject to a vote. This gives the community — usually those who hold governance tokens, specifically — an opportunity to evaluate the plans first, and then have a say in whether or not they go ahead.

Examples of a testnet in crypto

Aside from the Bitcoin testnet, which is now known as Testnet3, the best-known testnets are those for Ethereum. Unlike Bitcoin, which has just one official testnet, Ethereum has multiple — each of which is built differently. This gives developers the ability to scrutinize their applications in a variety of environments to ensure their stability and robustness.

This is particularly important for developers using the Ethereum network because of how much it has evolved over the years. Bitcoin still operates in mostly the same way as it did when it first launched, but Ethereum has undergone a number of significant changes, each of which has added new features and enhancements that developers can take advantage of.

Some of the biggest Ethereum testnets are:

• Sepolia: The default testnet for application development.
• Goerli: A testnet focused on validating and staking.
• Rinkeby: A testnet that uses the proof-of-authority consensus mechanism.

In addition, there are a number of testnets that were built for testing applications on Ethereum Layer 2 protocols. These include Arbitrum Goerli and Optimistic Goerli.

What is a mainnet?

A mainnet is a project’s primary blockchain network, or Layer 1. It is the foundation that everything else is built upon, and it allows users to transact using a decentralized system. In some cases, like with Ethereum, the mainnet may host applications that are powered by smart contracts — code that is executed automatically when certain conditions are met.

Mainnets are made up of a large network of nodes, which work together to keep the blockchain up to date, to verify transactions, and to ensure the network’s security. The two primary and most popular mechanisms for this are the proof-of-work (PoW) and proof-of-stake (PoS) protocols, which are used by Bitcoin and Ethereum, respectively.

Today, most mainnets are launched after a testnet, as opposed to the other way around. This ensures they can be evaluated and inspected, and that any issues can be addressed, before they are made available for public use. 

How does a mainnet work?

Depending on the consensus mechanism used, mainnets can operate very differently. For instance, PoW relies on mining, which is when powerful computers are used to solve complex cryptographic puzzles and validate new blocks. PoS relies on staking, which is when validators stake their tokens for a chance to verify new transactions.

For an in-depth explanation on mainnets, see our AAG Academy guide that explains blockchain technology and how it works.

Examples of mainnets in crypto

We’ve already mentioned two of the biggest and most popular mainnets within this guide: Bitcoin and Ethereum. These also happen to be the two most valuable cryptocurrency projects on the planet by some margin. But there are lots of other major mainnets in use today, including XRP, Monero, Litecoin, and TRON. Dogecoin also has its own blockchain network.

References

• Testnet
• Networks
• Inside the blockchain developers mind what is a testnet
• What are testnets