Bitcoin Education

Bitcoin Learning Sandbox

Explore wallets, UTXOs, fees, mempool priority, and block confirmations - all simulated locally. No real coins or nodes required.

Block Balance Mempool

Documentation

How the Bitcoin Learning Sandbox works - architecture, flow, and API reference.

Overview

Educational simulator - mock keys, UTXOs, mempool, RBF/CPFP, and blocks. No real Bitcoin node. You control mining.

1. Demo Wallet → Addresses

Create Demo Wallet makes mock keys + funded UTXOs. Choose a starting balance (1 / 3.15 / 5 / 10 BTC) before creating - default is 3.15 BTC across four practice coins. Generate New Address adds more receive addresses.

2. Coin Control

Like Electrum: tick which UTXOs to spend. Freeze coins to exclude them. Auto-select picks largest-first until amount + fee is covered. Unconfirmed change is only spendable via CPFP.

3. Transaction Builder

fee = fee_rate × vsize · change returns to your newest receive address. Enable RBF (BIP125) so you can bump fees later. Optional nLockTime is shown in the raw JSON.

4. Mempool, RBF & CPFP

RBF - replace a pending tx with a higher-fee version using the same inputs
CPFP - spend unconfirmed change with a high-fee child; package effective fee rate boosts the parent
Mining takes the top 6 by effective fee rate and can pull a CPFP parent with its child

5. Block Mining

Mine Next Block is manual. Confirmed txs leave the mempool; unconfirmed change becomes spendable as a normal UTXO.

6. Security Lessons

Address reuse - second spend from same address triggers privacy warning
Key exposure - exposed private key is swept on next block

Flow

Create Wallet → Coin Control → Broadcast (RBF) → optional RBF/CPFP → Mine Block → Confirmed

Demo Wallet

Create a practice wallet, pick a starting balance, generate receive addresses, and fund them with mock coins.

Start with

Click Create Demo Wallet to generate mock keys, Legacy + SegWit addresses, and starter coins for practice sends.

Transaction Builder

Electrum-style coin control: pick which UTXOs to spend, enable RBF, and optionally set nLockTime.

Coin Control

Selected: ·

No UTXOs yet. Create a demo wallet first.

Receiver Address

Amount (sats)

Fee Rate:

1200

RBF (BIP125)

nLockTime (optional)

Fee & Mempool Simulator

Estimated confirmation:

How mining works here: transactions stay in the mempool until you click Mine Next Block in Explorer. Each mine confirms the top 6 fee-rate transactions and removes them from the mempool.

Mempool is empty. Broadcast a transaction, then mine a block in Explorer to confirm it.

Blockchain Explorer

Mining is manual here - click Mine Next Block to confirm pending mempool transactions.

Recent Blocks

No blocks mined yet in this session.

Explorer Feed

Security Lessons

Address Reuse

Broadcast two transactions from the same address to trigger a privacy warning.

Private Key Exposure

Paste or expose your mock private key, then mine a block to simulate a sweep attack.