Build an App Start to Finish: the Plan

"I tick off my habits each day and see how many days in a row I have kept each one." That is the whole app. Reminders and charts belong to version two.

"Anyone in our house adds to the shopping list, and whoever is at the shop ticks things off." Two people, one list, both seeing the same thing. That is the job.

"A customer asks for a time slot, and the owner sees the request and says yes or no." Notice that it is a request. Taking payment, or promising a slot without a person checking, is a much bigger app.

"Someone answers ten questions and sees their score and which ones they got wrong." Leaderboards and accounts can wait.

• Today: your habits, each with a tick box and its current streak.
• Add a habit: a name and nothing else.

• The list: items, a box to add one, and a tick for bought.
• Join: how a second person gets onto the same list.

• Request a time: name, contact, the day and time wanted, and a note.
• The owner's inbox: every request, with accept and decline.
• The answer: what the customer sees or receives once the owner decides.

• Start: the quiz title and one button.
• Question: one at a time, with the answers to choose from.
• Result: the score and the questions missed, with the right answers.

Habit names and the days each was ticked. Only you ever see it. That is the easy case: the data can live in your own browser, with no server and no accounts.

The items and whether each is bought, shared between phones. Sharing is the hard part. The moment two devices must see the same data, you need a database on a server and some way to tell who is allowed in.

Customer names, contact details and requested times. That is personal information about other people, which makes this the most careful of the four. You need a database on a server, a login for the owner, and a plan for deleting old requests.

The questions and the right answers, which you write once and rarely change. If you do not keep anyone's score, there is nothing private to store at all.