Open guide · engineering notebook
Draw the Bitcoin app before you build it.
App Blueprint is a working notebook for people planning a Bitcoin wallet, tool or service. Read ten design principles, run a security and UX checklist, then let the wizard draft a one-page blueprint you can print, copy and argue with.
- 1Balance and its pending state are shown together.
- 2Receive and send are separate and plainly named.
- 3History is honest about unconfirmed entries.
- Drawing
- Wallet app, first pass
- Sheet
- A-01
- Rev
- A
- Scale
- NTS
- Drawn by
- You, with the notebook
- Status
- Draft
Sheet index
Four sheets, one notebook.
Start wherever your project is. If you only have an idea, begin with the wizard. If you have a prototype and a bad feeling, begin with the checklist.
| Sheet | Drawing | What it gives you |
|---|---|---|
| S-01 | Blueprint wizard | Five questions become a one-page blueprint: architecture diagram with trust boundaries, risk register, build order and a plain-text copy you can paste into a ticket or print. |
| S-02 | Ten principles | The reasoning behind the checklist. Each principle has a rule, the reason it exists, concrete practice, and a note on what usually goes wrong. |
| S-03 | Security and UX checklist | Twenty-eight checks, fourteen for security and fourteen for experience. Mark items done or not applicable and watch the progress bar. It remembers you on this device. |
| S-04 | Revision notes | Found a mistake or have a better idea? Draft a correction and send it by email. Nothing leaves your browser until you press send in your own mail app. |
Anatomy
Five parts of every Bitcoin app.
Whatever you are building, a payment passes through the same five parts. Select one to see what it does, the question worth asking about it, and the mistake that shows up most often in drafts.
Interface
- What it does
- Shows balances, collects intent, and teaches people what they are about to do. It is the only part most users will ever see, so it carries the whole burden of explaining the other four.
- Ask this
- Can a first-time user tell who holds the keys, and which actions cannot be undone?
- Usual mistake
- Copying banking-app patterns that imply an undo button or a dispute process the protocol does not have.
Fixed points
Constants that shape your screens.
These facts are long established and will not change under your feet. Each one has a consequence for interface design, which is why they are pinned to the drawing board.
- 21 million
Supply cap
The protocol caps total supply at 21 million bitcoin.
Design note: amounts are integers of the smallest unit, one hundred millionth of a bitcoin. Do math in integers and format at the edge. - ~10 min
Block interval
New blocks are targeted about every ten minutes, on average.
Design note: individual blocks can come much sooner or later, so "waiting" is a normal state. Design it, do not apologise for it. - 210,000
Halving cycle
The block subsidy halves every 210,000 blocks, roughly every four years.
Design note: the balance between subsidy and fees shifts over time. Never hard-code assumptions about fee levels. - SHA-256
Proof of work
Mining secures the chain with proof of work built on SHA-256.
Design note: users meet this as confirmations. Each confirmation makes reversal harder, and your copy should say so plainly. - UTXO
Coin model
Bitcoin tracks unspent transaction outputs, not account balances.
Design note: a balance is a sum you compute. Change outputs, dust and coin selection are real design surfaces. - 2008 / 2009
Whitepaper, genesis
The whitepaper appeared in 2008 and the genesis block followed in January 2009.
Design note: the protocol is older than most app frameworks. Prefer well-reviewed standards over novelty.
Method
Read, draw, check, revise.
The notebook is built to be used in a loop. Each pass leaves you with a sharper drawing and a shorter list of things you are afraid of.
Read the principles
Ten short entries explain why Bitcoin app design is different from ordinary fintech design: irreversible actions, user-held keys, public ledgers and slow finality.
Open the principlesDraw with the wizard
Choose an app type, custody model, platform, features and audience. The sheet on the right redraws as you answer, with a risk register and a build order to match.
Open the wizardCheck and revise
Walk the checklist against your blueprint, tick what is true today, mark what does not apply, and send us anything the notebook got wrong.
Open the checklist
Margin notes
What this notebook is, and is not.
Notebook rule: every box on the drawing needs an owner. If you cannot say who controls it, you have found your first risk.
Guidance only
Nothing here is a security audit, a legal opinion or financial advice, and no checklist can guarantee that an app is safe. Treat the output as a structured way to ask better questions, then get qualified review before real value is at stake.
Independent
App Blueprint is an independent project. It is not affiliated with any wallet, exchange, mining company, standards body or Bitcoin project, and it does not endorse any of them.
Private by construction
Every page is plain files. The wizard and checklist run in your browser, remember your answers only on this device, and send nothing anywhere. There are no accounts, no trackers and no uploads.
Ready to put the first line on the sheet?
It takes a few minutes, needs no sign-up, and ends with a page you can print or paste into your team's tracker.