GLOSSARY · BLOCKCHAIN & WEB3
Testnet
A testnet mirrors the consensus, gas and blocks of the live network with worthless tokens: it is where contracts, wallets and dApps are tried before mainnet.
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A testnet is a test network that reproduces how a blockchain works (transactions, gas, blocks and smart contracts) with tokens that have no economic value. It is used to deploy and test contracts, wallets and applications in a production-like environment before taking them to mainnet, the main network, where every transaction moves real value.
What is a testnet?
A testnet is a test network that reproduces how a blockchain works (transactions, gas, blocks and smart contracts) with tokens that have no economic value. It is used to deploy and test contracts, wallets and applications in a production-like environment before taking them to mainnet, the main network, where every transaction moves real value. According to ethereum.org, ETH on a testnet is supposed to have no real value.
Current Ethereum testnets (October 2026)
According to ethereum.org's networks documentation (updated September 23, 2026), Ethereum client teams currently maintain two public testnets:
- Sepolia (chain ID 11155111): the recommended default testnet for application development. It uses a permissioned validator set controlled by client and testing teams.
- Hoodi (chain ID 560048): for testing validation, staking and protocol upgrades before they reach mainnet. It launched on March 17, 2025 to replace Holesky.
There is also Ephemery, which resets to its initial state every 28 days. Holesky has been deprecated since September 2025, and Goerli is also listed as deprecated. Layer 2 networks publish their own testnets: for example, Arbitrum Sepolia (chain ID 421614), which according to Arbitrum's documentation runs on top of Sepolia.
Faucets: how to get test tokens
Testnet tokens come from faucets: websites where you enter your address and receive test ETH. ethereum.org links to faucets for Sepolia, Hoodi and Ephemery. That ETH pays the gas for test transactions, just as on the real network.
Testnet vs. mainnet
| Testnet | Mainnet | |
|---|---|---|
| Value of the tokens | None: you get them free from faucets | Real: ETH and tokens have a market price |
| Network identifier (chain ID) on Ethereum | Sepolia, 11155111; Hoodi, 560048 | 1 |
| Transaction cost | Gas paid in test ETH | Gas paid in real ETH |
| If something goes wrong | Fix it and redeploy | A deployed contract cannot be changed unless it was designed to be upgradeable, and a confirmed transfer cannot be undone |
| Network continuity | It may be reset or stop being maintained, as Goerli and Holesky were | Production network |
| What it is used for | Development, testing, pilots and rehearsing protocol upgrades | Launch and operation with real users and funds |
Since EIP-155, the chain ID is included in the data that is signed, and in typed transactions, such as EIP-1559 ones, it is a mandatory field: so a transaction signed for one network is not valid on another (EIP-155; Yellow Paper).
Checklist before moving to mainnet
Testing on a testnet does not replace reviewing the code. Before deploying to the main network:
- Automated tests for every function, including edge cases and expected failures.
- A full rehearsal on testnet with the same deployment script you will use on mainnet, plus end-to-end tests with the real wallet and front end.
- A code audit by an independent team, and fixes for whatever it finds: smart contract audit.
- Permissions reviewed: who is owner or admin, who can mint, pause or upgrade, and whether those keys sit in a multisig.
- Mainnet parameters: chain ID, addresses of external contracts (oracles, stablecoins) and gas limits, which differ from the testnet ones.
- After deployment: source code verified on the block explorer and an incident response plan.
In a regulated issuance, the testnet pilot also lets the issuer and its intermediaries validate investor onboarding and transfer restrictions before issuing.
Official sources: ethereum.org: Ethereum networks; Sepolia, official client repository; Hoodi, official client repository; Arbitrum: networks and chain IDs; EIP-155: simple replay attack protection; Ethereum Yellow Paper (mainnet chain ID); ethereum.org: upgrading smart contracts.
Framework verified as of October 15, 2026. At Unknown Gravity we deploy, test and audit smart contracts on testnet before taking them to mainnet: Ethereum and EVM development. Talk to us.
Learn more: What Is Blockchain and How Does It Work? Types, Real Examples and Limits
Explained simply
A testnet is a practice blockchain: it works like the real network, but its tokens are worth nothing. Developers use it to test contracts, wallets and apps without risking money, and test tokens are free from websites called faucets. Once everything works, the project launches on mainnet, the real network.
Testnet: key points
- A test network that mirrors mainnet with tokens that have no real value
- Ethereum maintains two public testnets: Sepolia (applications) and Hoodi (validators and staking)
- Holesky has been deprecated since September 2025, and so has Goerli
- Test tokens are free from faucets
- Testing on a testnet does not replace an audit before mainnet
Testnet: advantages
- No financial risk: mistakes do not cost real money
- Close to the real thing: the same transactions, gas and contracts as on mainnet
- Pilots with users: the team and early users try the product before launch
Testnet: disadvantages
- Not the real economy: test ETH has no value and network usage is different
- Networks that expire: Goerli and Holesky stopped being maintained, and Ephemery resets every 28 days
- Reliance on faucets to get test tokens
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