Signet

Also called: signet network, default signet, custom signet, Bitcoin signet, signet coins.

Signet is a Bitcoin test network, defined in BIP 325, where blocks must be signed by designated keys, making it far more predictable than testnet.

Signet is a Bitcoin test network where, in addition to proof of work, every block must carry a valid signature from a designated key or set of keys. That gives it steady block production and no surprise reorganizations, so developers can test software over long periods without the disruption common on testnet.

How it works

BIP 325, by Karl-Johan Alm and Anthony Towns, adds one consensus parameter, the challenge: a script such as a single key or a k-of-n multisig. A block is valid only if the witness commitment in its coinbase transaction includes a solution (a signature) that satisfies the challenge. The signature is checked using two virtual transactions built from the block's data, and it doesn't commit to the nonce, so miners can still grind proof of work after signing.

Different challenges create different signets. All signets share one genesis block, and each network's 4-byte message start is derived from its challenge, giving every signet its own network identity. Proof of work still applies, but at a very low minimum difficulty (about 0.0011).

Why it matters

• Predictable. BIP 325 aims to be "reliably unreliable": block signers can even trigger rare events like a 6-block reorg on purpose for testing.
• Shared and long-lived. Unlike regtest, where one developer creates blocks for free on a private chain, a signet is shared by many independent parties.
• Testing upgrades. Custom signets let developers try proposed soft forks. BIP 95 notes that the BIP 54 rules were already enforced on signet through Bitcoin Inquisition when it was written.

Outsiders can't mine signet blocks, so testers get coins from faucets. Signet uses the same address formats as testnet: tb1 for SegWit addresses and tpub for extended keys.