Your idea in one sentence · Build Your Card App

Every app in this guide starts the same way: one sentence. Not a page, not a list of features. If you can't say your idea in one breath, it is either too big for a first app or not clear yet. Both are fixable, and this step fixes them.

The shape of the sentence

"[App] helps [who] [do what] so that [why]."

For the example app: "Binder helps collectors see what each card and their whole collection is worth, so they stop guessing."

Compare that with two sentences that don't work:

Too big: "Binder is an app for everything about cards: collecting, buying, selling, grading, scanning, a marketplace and a community."
Too vague: "Binder makes collecting better."

Small and specific wins every time. A small app can be on your phone in weeks. You can always add more later. A big idea is a list of small apps, and you build the first one first.

Start your notes

You will collect notes in every step of this part. Use the simple notes app that came with your computer, which Part 1 showed you how to open. Paper works too, if you prefer.

On a Mac

Open Notes: hold Command, press Space, type notes, press Return.
Click the new note button at the top. It looks like a square with a pencil.
Type Binder notes on the first line, using your app's name. That line becomes the note's title.
Leave the note open. Notes saves by itself.

On a Windows PC

Open Notepad: press Windows, type notepad, press Enter.
Type Binder notes on the first line, using your app's name.
Press Ctrl + S. A save box opens. In the File name box type Binder notes, make sure Documents is the folder shown at the top, and click Save.
Leave the file open. Press Ctrl + S now and then as you add to it. To find it later, open File Explorer, click Documents, and double-click Binder notes.

Let Claude sharpen it

Pick the kind of card app you want. Each choice below is a complete message, ready to send. Open a new chat in Claude, copy the one closest to your idea, change any word you like, and send it. The rest of this part refers back to your choice.

Collection tracker, like the example app: your cards with set, number and condition, what each one is worth, what the collection is worth, and a wishlist.

Seller's app: for card shows and deals. Your stock with what you paid, buying and selling at a table, a screen the customer may see, and show totals.

Shop app: for a card shop. Your stock of singles and sealed products, a storefront page customers can open, and the want lists they leave with you.

Read the three versions. Pick the one that sounds most like you, and change any word you wouldn't say. If Claude said the idea is too big, take its advice: cut until one sentence fits.

Copy your final sentence into your notes under the heading "One sentence". Under it, write which kind you picked: "Kind: collection tracker", "Kind: seller's app" or "Kind: shop app".