From Spreadsheet to SaaS: How to Build an AI Web App with Google Sheets

Have you ever wondered if you could build a real, full-stack web application using only Google Sheets? Not just a simple dashboard, but a dynamic, multi-user app that connects to a powerful AI, saves user data, and looks like a professional SaaS product?

I’m thrilled to say the answer is a resounding yes.

Today, I want to take you behind the scenes of my latest project at Kaydiem Script Lab: the AI Intuition Trainer. This is the story of how a simple idea evolved into a complete digital product, built entirely on the surprisingly powerful (and free) Google ecosystem.

And the best part? I’ve turned the whole thing into a template so you can launch your own AI web app in under 5 minutes.

The platform of choice? My favorite secret weapon: Google Apps Script. 

This stack is incredibly powerful because it’s virtually free to start and infinitely scalable for thousands of users without any server costs.

1. The AI Challenge Engine

The heart of the app is the generateAiChallenge function in Code.gs. It uses Google's built-in UrlFetchApp service to send a carefully crafted prompt to the Mistral AI API. The AI then returns a perfectly formatted JSON object with a unique question, four options, and the correct answer. This means the game never gets old.

2. The Google Sheet Database

A Google Sheet is a surprisingly effective database for projects like this. We use two tabs:

1. UserData: Stores each user's email, name, score, level, and streak.

2. ChallengeLog: Keeps a historical record of every answer for every user, which powers the progress chart.

The script uses functions like getSheetByName() and appendRow() to interact with the data in real-time.

3. The Multi-User Login System

This was the trickiest part. To make the app work for everyone, not just me, the script had to be deployed with a critical setting: Execute as: User accessing the app. This forces every new visitor to authorize the app with their own Google account, creating a secure and personalized experience. We also had to change the Google Sheet's sharing permissions to "Anyone with the link can edit" so the script, running on behalf of different users, could write data to it.

After weeks of coding, debugging, and UI design, the final product was live. A sleek, multi-user web app with a beautiful "Zen" theme, persistent stats, and an endless supply of AI-powered challenges.

It felt too good to keep to myself. I realized the true value wasn't just the game itself, but the underlying template. This was a complete, working "business-in-a-box" for anyone who wanted to launch their own AI-powered tool on the Google ecosystem.

I've spent the time packaging this entire project into a simple, copy-and-paste template so you can bypass the difficult debugging and go straight to launching.

When you get the template, you receive a PDF guide with a link. One click, and the entire application—the Google Sheet database and all the Apps Script code—is copied directly into your own Google Drive.

The 5-minute setup process is simple:

• Copy the template.

• Get your own free API key from OpenRouter.

• Deploy the app.

That's it. You'll have your own private, fully functional version of this app, ready to use or share.