What is testnet

In the crypto world, a testnet (“test network”) is a playground version of a blockchain that:

• Runs the same software and consensus rules as the main network (mainnet)—so it’s realistic for testing smart contracts, wallets, nodes, upgrades, etc.
• Uses special test‑tokens with zero market value, so there’s no financial risk if you break things or spam transactions. You can usually get these tokens for free from a “faucet.”
• Often resets or can be wiped when major protocol changes are introduced, making it easier for devs to start fresh.
• Lets core developers trial protocol upgrades (hard forks, EIPs, BIPs, etc.) before putting them in front of real money.

Why you’d care

• Developers deploy contracts or dApps there first to catch bugs cheaply.
• Node operators can practice configuration and monitoring.
• Power users can rehearse complicated DeFi trades or wallet flows without risking assets.

Well‑known examples

Mainnet	Common Testnets (as of 2025)	Notes
Bitcoin	testnet3, signet	Signet is newer, easier to spin up custom test environments.
Ethereum	Sepolia, Holesky	Sepolia is the primary lightweight testnet after Goerli wind‑down.
Polygon	Mumbai	Mirrors Polygon PoS chain.
Solana	Devnet, Testnet	Devnet resets more frequently.

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If you’re thinking of building or experimenting, let me know what chain or toolset you’re using—I can walk you through getting test tokens or setting up a local node.