Catch the Mistake

Inspiration

Percentage mistakes can look completely reasonable, especially when VAT is already inside a total. Most AI tutors simply provide another answer. I wanted an experience that makes the learner do the meaningful reasoning and finish with a feeling of accomplishment.

What it does

Catch the Mistake turns GPT-5.6 into the apprentice. It makes exactly one believable error. The learner selects the faulty step, explains the repair in plain language, and proves the idea on fresh numbers.

Learners can also upload a percentage-problem screenshot. GPT-5.6 vision transforms it into the same Find, Explain, Prove learning loop.

How we built it

I made the central product, learning, accessibility, and design decisions with ChatGPT Work. Codex translated the approved direction into the working interface, integrated GPT-5.6 vision and structured output, added validation and accessibility tests, and prepared the secure public deployment.

The app has no accounts, analytics, or persistent learner records. Screenshots are sent only after an explicit action.