Below is a clean, practical walkthrough using Bitcoin Core + bitcoin-cli to:

1. create a testnet address
2. export the wallet’s extended public key (xpub / tpub)
3. save it as an “xpub file” suitable for watch-only wallets or your own signer/web app

I’ll show descriptor-based (modern, correct) methods first, then explain what the data means.

Prerequisites

• Bitcoin Core v23+ (v24/25 fine)
• Testnet enabled
• A descriptor wallet (default in modern Core)

Start bitcoind on testnet:

bitcoind -testnet

(or add testnet=1 to bitcoin.conf)

1️⃣ Create a testnet wallet (descriptor wallet)

bitcoin-cli -testnet createwallet "testwallet"

Check it’s loaded:

bitcoin-cli -testnet listwallets

2️⃣ Create a testnet address (bc1-style on testnet → tb1...)

Native SegWit (recommended)

bitcoin-cli -testnet getnewaddress "receive" bech32

Example output:

tb1q7s8m4h0u7j3x5p8k8n0d4z2...

This is:

• P2WPKH
• testnet
• SegWit v0

3️⃣ Get the wallet’s extended public key (XPUB → TPUB)

Bitcoin Core does not expose xpubs directly anymore — it uses descriptors.

You extract the xpub from descriptors.

Step 3.1 — List wallet descriptors

bitcoin-cli -testnet listdescriptors

You’ll see output like:

{
  "wallet_name": "testwallet",
  "descriptors": [
    {
      "desc": "wpkh([d34db33f/84h/1h/0h]tpubDC5J...xyz/0/*)#abcd1234",
      "timestamp": 1680000000,
      "active": true,
      "internal": false
    },
    {
      "desc": "wpkh([d34db33f/84h/1h/0h]tpubDC5J...xyz/1/*)#efgh5678",
      "internal": true
    }
  ]
}

Step 3.2 — Identify the tpub

Focus on this part:

[d34db33f/84h/1h/0h]tpubDC5J...xyz/0/*

Meaning:

This tpub... is the expub you want.

4️⃣ Save the expub to a file (watch-only export)

Create a file (example: testnet-expub.txt):

# Bitcoin Core testnet expub
# Wallet: testwallet
# Script: P2WPKH (BIP84)
# Network: testnet

[d34db33f/84h/1h/0h]tpubDC5Jxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

This is exactly what:

• Specter
• Sparrow
• your air-gapped signer
• your web PSBT generator

will consume.

5️⃣ (Optional) Export both receive + change branches

Include both:

# Receive
[d34db33f/84h/1h/0h]tpub.../0/*

# Change
[d34db33f/84h/1h/0h]tpub.../1/*

Your signer should recognize /1/* as change.

6️⃣ (Optional) Taproot (P2TR, BIP86) expub

Generate a Taproot wallet address first:

bitcoin-cli -testnet getnewaddress "taproot" bech32m

Then list descriptors again:

bitcoin-cli -testnet listdescriptors

You’ll see:

tr([d34db33f/86h/1h/0h]tpubXXXX/0/*)

Export that tpub as well.

7️⃣ Verify the expub produces the same address

Use deriveaddresses:

bitcoin-cli -testnet deriveaddresses \
"wpkh([d34db33f/84h/1h/0h]tpubXXXX/0/*)" "[0,5]"

You should see addresses matching getnewaddress.

8️⃣ Why Bitcoin Core does this (important)

Bitcoin Core:

• no longer exposes xpubs directly
• uses output descriptors to avoid ambiguity and bugs

Descriptors are:

• safer
• explicit
• exactly what hardware wallets and PSBT flows expect

Your signer design is aligned with this.

9️⃣ Summary (copy/paste checklist)

# create wallet
bitcoin-cli -testnet createwallet "testwallet"

# create address
bitcoin-cli -testnet getnewaddress "" bech32

# extract expub
bitcoin-cli -testnet listdescriptors

Then save:

[d34db33f/84h/1h/0h]tpub.../0/*
[d34db33f/84h/1h/0h]tpub.../1/*