Teaching tool · DEMO ONLY

Transaction lab

Build a toy payment the way Bitcoin does it: pick inputs, name an output, pay a fee, and keep change. Nothing here is a real transaction. Nothing here changes your paper-trading cash or the wallet sandbox.

TEST-ONLY

DEMO ONLY — not a real wallet, not Bitcoin mainnet, never enter a real seed or mainnet address here. BitBuddy will never ask for your real seed.

What this is

  • This page spends toy UTXOs: fake outpoints and classroom satoshis.
  • A real payment consumes unspent outputs and creates new ones, minus a fee.
  • Change is leftover that comes back to you. The fee is leftover miners collect.
  • Nothing here is a Bitcoin transaction. Paper-wallet cash is not touched.
  1. UTXOs
  2. Build
  3. Broadcast
  4. Mempool
  5. Confirmed

Input

A previous unspent output (UTXO) you are spending. You pick which coins to use.

Output

A new piece of value this payment creates — typically one to the recipient.

Change

What comes back to you: inputs minus the send minus the fee.

Fee

A bid to be included in a block. Higher sats/vByte usually waits less.

Demo address that owns these UTXOs

bbtest1txlabclassroom01

classroom satoshis — not Bitcoin, not paper cash. Prefix bbtest1 is on purpose.

1. Select inputs (toy UTXOs)

Bitcoin does not keep one “account balance.” Value sits in unspent outputs. Check the pieces you want this payment to consume.

An input is a UTXO you are spending. Fake outpoints like TOYOUT-…:0 stand in for a previous transaction’s output index. They are not mainnet.

2. Amount, destination, and fee

Pre-filled with a second bbtest1… classroom address.

Fee rate (sats / vByte)

Size is a classroom estimate: 10 + 68 per input + 31 per output (always 2 outputs: recipient + change). Fee = vBytes × rate.

3. Change math (live)

inputs − send − fee = change. If change would be negative, you need more inputs or a smaller send.

Selected inputs 130,000
Send − 60,000
Fee (208 vB × 8) − 1,664
Change back to you 68,336

This draft can broadcast. Change is a new output you still control.

The fee is not a separate coin you attach. It is whatever is left after the outputs are named. Miners keep that leftover.

Keep going

This is not the paper wallet

The dashboard paper wallet is a spreadsheet of practice cash. The wallet sandbox is a key/address lab. This page is how a send becomes a transaction. Three tools; none of them move real money.

Create a free account to paper trade when you want a practice balance. This lab stays open either way.

Create a free account to paper trade Open the wallet sandbox Back to transactions lesson