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The AI That Tests Your App Before It Says "Done"

Every AI app builder says “Done.” From today, JustCopy has to prove it: it uses the app it just built, on screen, and fixes what fails before you lift a finger.

September 7, 2026•6 min read

One real run, unedited apart from speed: a gratitude journal built from one sentence, five checks, one failure, the free fix, the passing retest.

“Done” was a claim

Last week a paying customer wrote to us about the app she had built: the photo upload did not work, and the things she typed did not show up where she expected them. We read her whole conversation. The agent had written “Done” five times about a page it had never opened. Every one of those was a guess.

Generating a page and checking that a page works are different jobs, and every AI builder we know of does only the first. The person who finds out whether the app works is the owner, or worse, the owner’s first customer.

So we changed the rule. An app now gets used before the agent may call it done.

What happens after every build

  1. 1

    Build

    You type one sentence. The app appears on screen, usually in well under a minute.

  2. 2

    Plan

    A short list of checks is written from the app itself, in your words: "Add an entry", "Attach a photo", "Delete it", "Reload and check it is still there".

  3. 3

    Use

    The app pane gets a breathing blue border and a cursor starts using your app: it types, presses Save, drops in a sample photo, deletes an entry, reloads the page.

  4. 4

    Judge

    After each check the words on the page are compared with what should be there. A tick or a cross lands in the chat, with a plain reason.

  5. 5

    Fix

    A cross goes straight back to the agent with the failing step and the page errors. It fixes the problem and only the failed checks run again. This costs you nothing.

The border and the cursor are deliberate. When an AI takes over your browser you can see it working; we wanted the same feeling for your app. Nothing is hidden, and you can watch every tap land.

What it found on day one

We ran it on a fresh app and on a copy of the customer’s app. Both of her complaints were found and fixed without a person reading the transcript. Three of the things it caught:

A text box that reset after every letter

The agent had defined the app's parts inside the page's own drawing routine, so the box was rebuilt on every keystroke and only the first letter survived. The test said exactly that, in words, and the fix landed a minute later.

A delete that did not stick

Entries were created with a temporary id, so deleting one removed the wrong record. No visitor would have reported this; they would have left.

Our own production bug

The first recording of the demo video failed the photo upload check. The cause was on our side: the service that stores app files had lost a permission, so every photo upload in every generated app had been failing. The test found it before a second customer did.

The rules it follows

  • It never signs in or out. Your preview shares your JustCopy session, so a test that signed out would sign you out too.
  • Everything it creates is removed when the run ends: the sample entries, the sample photo.
  • It does not pay, email or text anyone. Checks that would need a card, an inbox or a phone are listed as skipped with a reason.
  • Every action is visible. Nothing happens off screen, and the chat says what was tried and what was seen.

What it does not do yet

  • Dropdowns, date pickers and checkboxes are not driven yet, only typing, clicks, uploads and reloads.
  • The checks run in your studio, on screen. A silent rerun before publish, and a daily sweep of published apps, are next.
  • Ambiguous outcomes (a photo that appears but looks wrong) still need your eyes.

Questions

Does the testing phase cost anything?

No. A build counts toward your daily builds as before. The checks and any fix they trigger are free.

Can it see my data?

It works inside your own preview, as you. It creates its own sample entries and removes them after. It does not read anything it did not create.

What if I do not want it to run?

Let it finish or send your next message; a new build takes priority. Every check is visible, so there is nothing to undo.

Which apps does it test?

Every app the agent builds or changes. Small wording and colour changes are applied directly and do not need a test.

Type it. Watch it build. Watch it prove itself.

One sentence becomes an app, the app is tested in front of you, and one tap puts it live. Free to start.

Build yours free