Spreadsheet Formula Checker (App Maxxing, early release)

EARLY RELEASE: PLEASE READ BEFORE BUYING

• This app needs your own OpenAI API key. It will not run without one, and a ChatGPT subscription does not include one.
• It is an early release that still needs further testing. So far each app has passed our own offline tests, and has been run on its built-in sample against the live service on both models (October 2026). It has not yet been tried on a wide range of real files of different kinds and sizes. You may meet faults.
• Please tell us what you find after you buy: email kit376351@gmail.com with the subject "Maxxing feedback". Every report is read, and fixes are sent to buyers free.
• If we cannot get it running for you, email us within 14 days for a refund of the app price.

Look for the odd formula, the typed-over number and the total that misses a row in your own Excel workbook.

WHAT IT DOES

Add one Excel workbook of your own (.xlsx). The app reads every formula on your computer and looks, in code, for the things that go wrong in real workbooks: a formula that breaks the pattern of its column or row, a number typed over a formula, a total whose range stops short of the data or runs past it, a typed number buried inside a formula, error values, numbers stored as text, formulas that point at empty cells, hidden rows, columns and sheets, headings whose units do not fit the formula (millimetres added to metres), and formulas that refer back to themselves. The workbook file itself is not uploaded; what the app takes from it is sent to OpenAI, as follows. The model is given the app's findings, the headings and row labels, the formulas, and a small sample of values, or no values at all if you tick the box: the button 'See exactly what will be sent' shows every word. The model explains what the workbook seems to be for, says which findings are likely to matter and how to fix them, and may suggest logic problems of its own. Every suggestion is then checked against your file in code: one that names a cell that is not in the workbook is not shown, and one that quotes a formula wrongly is marked 'not confirmed'. You get a count of what was checked and what was not, a findings table that says for each row whether it was found by the app or suggested by the model, the odd formula side by side with its neighbour with the difference marked, an Excel file of the findings and a Word report. For educational purposes only.

HOW IT IS BUILT

• The app's own code does the finding, the arithmetic and the unit conversions. The AI is used only for what code cannot do, and what it says is checked against your file.
• Anything the app cannot find in your file is marked "not found in the file", not trusted.
• The cost is shown before each run and after it, with a limit you set for one run.
• No verdicts: the app never says pass, fail or compliant. It shows you what it found and where.

WHAT YOU NEED

• Windows, Mac or Linux, and free Node.js 18 or newer
• Your own OpenAI account with API access and a key (platform.openai.com). This is separate from a ChatGPT subscription.
• You pay OpenAI for what you use, on top of the price of the app. In our own tests on a short sample file, a run of this app cost about 16 cents. Longer files cost more.
• The app uses OpenAI's GPT-6 Astra model. In Settings you can switch to a cheaper model at about a fifth of the price.
• About ten minutes of setup. A step-by-step guide is included.

HONEST LIMITS

These are suspicious cells, not proof of an error, and a blank findings list does not mean the workbook is correct. The app looks at how the workbook is built, not at whether the engineering or the science behind it is right, and it does not recalculate anything. Macros, charts, pictures, pivot tables, conditional formatting, data validation and links to other workbooks are not read. Files saved as .xls, .xlsm or .xlsb must be saved as .xlsx first. Formulas that use INDIRECT, OFFSET, table references or names the app cannot follow are only partly checked, and the app says how many there are. The unit check relies on units written in your headings, such as 'Span (m)'. Headings and row labels are always sent to the model, so do not use a workbook whose labels you may not share.

For educational purposes only, and for your own research and your own documents. The app points things out for you to check: it does not certify, approve or sign off anything, what the AI writes can be wrong, and it is not a substitute for review by a qualified person. You are asked to accept this when you first open the app.

PRIVACY

The app runs on your computer. It says before each run exactly what will be sent to OpenAI, under OpenAI's terms, and what stays on your computer; nothing is sent to us. Use it only with documents you are allowed to send to an AI service: not an employer's or customer's confidential documents, not export-controlled material, and not someone else's unpublished work. Your key is stored only on your computer and is sent only to OpenAI.

WHAT IS INCLUDED

The app (a zip file), start files for Windows, Mac and Linux, a sample to try, a setup guide and a README. Kitson Workshop is not affiliated with or endorsed by OpenAI.

REFUNDS

Digital download. If we cannot get it running for you, email kit376351@gmail.com within 14 days for a refund of the app price. Credit you bought from OpenAI is theirs to refund or not.

FEEDBACK AND IDEAS

Email kit376351@gmail.com with the subject "Maxxing feedback" to report a fault or tell us what worked. For a new app idea, use the subject "Kitson idea".