A Bitcoin address is a public receipt. Anyone can read your transactions forever. Most people accept that. What they don't think about is the other half: the records you actually need - what you paid, when, and your cost basis - usually live inside a KYC exchange account you don't control.
Why it matters: at some point you'll need cost basis (taxes, planning, proving what you hold). If it only exists in an exchange that can deprecate exports, lock the account, or tie every number to your identity, you don't really have records - you have access that can be revoked.
What I built: the Bitcoin Holder Toolkit. A plain Excel / Google Sheets file you own. Log each buy, track cost basis per lot, and see your whole stack in one place - offline, no account, no subscription. It's recordkeeping you control, nothing more. It is not a privacy tool and it is not tax advice; for filing decisions use a qualified professional.
Who it's for: self-custody holders who want their own records instead of trusting an exchange dashboard.
(Context: follows EP14 on Bitcoin privacy - what the chain sees and what it doesn't.)