Write the one sentence the app has to earn

Somebody asks what the app is for. You answer one way on the Monday and a different way on the Thursday. Both answers are honest. It started with a loose paragraph typed into the builder, and screens that came back looking finished.

Not a naming problem. The decision was never made, and no builder on earth is going to make it for you.

An app you cannot say in one sentence still gets built. It just gets built three or four times.

The rules

The sentence names one person, one moment, one outcome.

Write it in this shape and nothing looser: this app lets NAMED PERSON do ONE THING at ONE MOMENT so that OUTCOME. Fill all four slots. A slot left vague makes the app vague in exactly that place. You find out in week three, when somebody asks you to change it.

If the sentence needs an "and", you have two apps.

That is two verbs, two people and two moments. Nobody finishes two apps at once when they have never finished one. Pick the half you can finish. The other half goes on the refusal list where you can see it. Not in your head, where it quietly grows.

The named person is a human with a phone number.

Not a segment, not a persona, not "small business owners", not a market you read about on a podcast and have never fed, invoiced or argued with. You need someone you can text tonight. Every decision from here gets settled by what that one person actually does. A persona decides nothing.

Write the refusal list before the feature list.

Four to six things this app will not do in version one. No admin panel, no exports, no notifications, no second user type. Refusals are the only part of scoping that holds under pressure. They are written down before you start wanting them.

Scope it to something one person can use inside a week.

Not demo, use. If the first honest use is a month away, the sentence is still too big. You will lose the person long before the app is ready for them.

Do it now

Open a plain text file and write your sentence in the four-slot shape. Put the name and phone number of the person underneath it. Then write four refusals.

Now pressure test it against something with no reason to be kind. Paste this into any chat model:

Here is my app sentence: <paste it>
Name every assumption hiding in it.
List the parts of it that would be true of ten other apps.
Rewrite it so it is false for every app except mine.
Do not add features. Do not be encouraging.

Take the rewrite only if it comes back shorter than what you wrote. Then say the sentence out loud to the person you named. Say nothing else. Let them repeat it back in their own words.

A worked example

Say you run a three-chair dog-grooming salon. Most of the diary is regulars who come back every six to eight weeks. Rebooking happens at the till, on paper, while a wet dog pulls at the lead. Often it does not happen at all. The slot goes to somebody else.

Sentence:  This app lets Janet Hale rebook Biscuit's next groom
           on her phone as she leaves the salon,
           so that her six-week slot is held before the diary fills.
Person:    Janet Hale, 07700 900412. In every six weeks with Biscuit.
Refuses:   1. No payments or deposits
           2. No sign-up for new customers
           3. No text or email reminders
           4. No staff rota or chair planning
Said back: she books Biscuit's next one on her phone on the way out,
           and keeps her six weeks.
Slots:     person present, thing present, moment present, outcome present. Pass.

One sentence, one name, four refusals. Still no screens.

The failure you will hit

The sentence will grow. It grows at the exact moment building gets boring. Usually around day three. It arrives as a small reasonable addition from someone you like. You agree before you have noticed. The tell is the word "and". Read your sentence out loud once a day and check it for clauses. If it has gained a clause, delete the clause, not the day's work.

Not for you if

You want to build something impressive rather than something that gets used. This step takes an hour of your time and produces no screens. If that reads as wasted time, you will skip it. Then you build for a month and find out the slow way.

You have a sentence and a refusal list. Step two turns that sentence into entities. The Vault is the paid library from there.