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Learning objectives

  • Understand the purpose and power of Bitcoin Core’s regtest mode
  • Set up a private, fully controlled Bitcoin network
  • Mine blocks and confirm transactions instantly
  • Use regtest for API testing, integration flows, and simulations

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Why Regtest matters

regtest stands for Regression Test mode. It is a fully offline, developer-first Bitcoin network that:
  • Has no network peers (your node is the entire network)
  • Lets you mine blocks instantly
  • Offers free test coins and instant transaction confirmation
  • Works perfectly with automated testing, CI flows, and local wallets
For building real Bitcoin apps, regtest is the fastest and safest sandbox.

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Setting up a fully isolated Bitcoin environment

Start your node in regtest mode:
This creates:
  • ~/.bitcoin/regtest/ as your data directory
  • A zero-block chain, ready to mine
  • No connections to testnet, mainnet, or the internet
You can confirm the mode using:
Look for “chain”: “regtest”

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Mining blocks instantly

Regtest allows manual block generation. First, create a wallet and get a new address:
Now mine 101 blocks (to unlock coinbase rewards):
This gives you spendable BTC for testing. You can generate 1 block at a time to simulate confirmation behavior.

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Sending transactions instantly

With freshly mined coins, you can now send BTC. Regtest has no fee history, so make sure fallbackfee=0.0001 is set in bitcoin.conf (see module 1):
Check mempool:
Confirm instantly by mining a block:
Now check the recipient’s balance, from the wallet that holds <destination>:

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GUI alternative: Polar

Polar is a desktop app that sets up a regtest Bitcoin + Lightning network for you using Docker. Why use it? No terminal needed Visual interface for nodes, wallets, payments Supports Bitcoin Core + LND + Core Lightning 🖥️ If you prefer a GUI for testing, Polar is highly recommended. It is especially useful for team demos, education, and debugging. Install it via:
  1. macOS: brew install —cask polar
  2. Linux: .AppImage from GitHub
  3. Windows: .exe installer
You can still inspect logs, addresses, and transactions under the hood.

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Activity

Set up a regtest sandbox from scratch:
  1. Start bitcoind in regtest mode.
  2. Create a wallet named activity_wallet, generate 101 blocks (replace <your_address> with an address from the new wallet).
  3. Send 2 test transactions (replace <destination_1>, <destination_2> with valid addresses).
  4. Mine 1 block to confirm (use the same <your_address> as before or another address in activity_wallet).
  5. Use listtransactions to view history.
Wallets that understand UTXOs deeply will control fees, preserve privacy, and scale cleanly over time. Bonus: Try doing the same flow inside Polar