How I Built a Functional SaaS MVP in Just 4 Days with AI
Z
Zack Saadioui
8/11/2025
So, you've got a SaaS idea. That's the easy part, right? The hard part is turning that idea into something real, something tangible, without getting lost in a development cycle that lasts for months & costs a fortune. I've been there, & honestly, it can be a real grind.
But what if I told you that you could build a functional SaaS MVP (Minimum Viable Product) in just four days? It sounds a little crazy, I know. But with the right tools & a focused plan, it's totally doable. I'm going to walk you through a step-by-step diary of how I did it using an AI-powered code editor called Cursor. This isn't just theory; this is a real-world account of going from zero to a deployed MVP in under a week.
Let's get into it.
First, a Little About the Tools
The star of this show is Cursor. Think of it as a supercharged version of VS Code that's been rebuilt from the ground up with AI at its core. It’s not just an add-on; it's a completely different way of coding. Cursor can understand your entire codebase, suggest multi-line edits, answer questions about your code, & even write a ton of it for you. This is what makes a 4-day MVP possible.
We'll also be using a few other things:
Next.js: A popular React framework for building the frontend.
Supabase: An open-source alternative to Firebase for our database & backend needs. It’s super easy to get started with.
Vercel: For deploying our app.
The goal here isn't to build a perfect, feature-packed product. The goal is to build an MVP. An MVP is the most basic version of your product that solves a core problem for your target audience. It's about testing your idea, getting feedback, & validating that you're on the right track before you invest a ton of time & money.
Day 1: The Blueprint & the Face
Alright, Day 1. The excitement is high, the coffee is brewing, & the possibilities feel endless. Today is all about laying the groundwork & building the user interface (UI). It’s important to get the UI done first because it gives you a visual target & helps you understand what you actually need to build on the backend.
Morning: Planning & Setting Up Cursor
The very first thing I did was get my head straight. I grabbed a notebook & sketched out the core functionality of my SaaS. What's the one main problem I'm solving? Who am I solving it for? What are the absolute must-have features for the MVP?
Once I had a clear idea, I set up my project in Cursor. This is a crucial step. Cursor has a feature called ".cursorrules" which is basically a set of instructions for the AI. I created a new
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.cursorrules
file in my project's root directory & laid out the plan. I told the AI about my project, the tech stack I was using (Next.js, Supabase), & any specific coding conventions I wanted to follow. This helps the AI generate much more accurate & relevant code.
Afternoon: Building the UI with a Screenshot
Now for the fun part. I'm not a designer, so I found a UI that I liked on Dribbble, took a screenshot, & gave it to Cursor. I literally just said, "Build me a UI that looks like this, but with these specific text elements & buttons."
And you know what? It did a pretty amazing job. It generated the Next.js components with Tailwind CSS, & with a few tweaks & prompts, I had a beautiful, responsive UI up & running. It wasn't perfect, but it was a solid 80% of the way there in a fraction of the time it would have taken me to code it from scratch.
By the end of Day 1, I had a clickable, albeit static, frontend. I could see my app coming to life, which was a HUGE motivator.
Day 2: The Brains of the Operation
Day 2 is all about the backend. This is where we give our pretty UI a brain. We need a database to store our user data & the core information our app will handle.
Morning: Database Schema with Supabase & Cursor
I decided to use Supabase for this project because it's so developer-friendly. I went to the Supabase website, created a new project, & then it was time to design the database schema.
Here's where Cursor came in again. Instead of writing a bunch of SQL, I just described what I needed in plain English. I opened up the SQL editor in Supabase & then, in Cursor, I wrote a prompt like: "Create a Supabase SQL schema for a to-do list app. I need a 'users' table with columns for id, email, & created_at. I also need a 'tasks' table with columns for id, user_id (as a foreign key to the users table), task_title, is_completed, & due_date."
Cursor generated the SQL script, I copied it, ran it in Supabase, & just like that, my database was ready. No fuss, no syntax errors, just a clean, functional database structure.
Afternoon: Connecting the Dots
Now that I had a database, I needed to connect it to my Next.js app. This involved setting up the Supabase client in my project & creating the API routes to handle the communication between the frontend & the backend.
Again, I leaned heavily on Cursor. I'd ask it to "create a new API route in Next.js to fetch all tasks for a specific user from the Supabase database." And it would spit out the code. It wasn't always perfect, but it gave me a massive head start. I had to do some debugging, of course, but that's just part of the process.
At the end of Day 2, I had a working backend connected to a database. I could now, in theory, create, read, update, & delete data. The app was starting to feel real.
Day 3: Bringing It All Together
Day 3 is where the magic really happens. We have a face (the UI) & a brain (the backend), & now it's time to connect them & build out the core logic of our SaaS.
Morning: Implementing Core Features
My to-do list app needed a few key features: user authentication, the ability to add new tasks, mark them as complete, & delete them. I tackled them one by one, using Cursor as my coding partner.
For user authentication, I used Supabase's built-in auth. It's incredibly easy to set up. I asked Cursor to "implement Supabase authentication in my Next.js app with login & signup pages." It generated the forms, the logic to handle the auth flow, & even the protected routes that only logged-in users could access.
For the task management features, I built out the functions to interact with the API routes I created on Day 2. For example, when a user clicks the "Add Task" button, it sends a request to the backend to create a new task in the database.
This is also where a tool like Arsturn could come in handy down the line. Once the MVP is live & I start getting users, I'll inevitably have questions. I could use Arsturn to build a no-code AI chatbot trained on my documentation. This would allow users to get instant support & answers to their questions 24/7, freeing me up to focus on development. It's a great way to handle customer service for a small team (or a team of one!).
Afternoon: Debugging & Refinement
As I was building out the features, I was constantly testing & debugging. This is where Cursor's "chat with your codebase" feature is a lifesaver. I could highlight a piece of code & ask, "Why is this not working?" or "Is there a more efficient way to write this?" The AI would analyze the code in context & give me suggestions. It's like having a senior developer looking over your shoulder.
By the end of Day 3, I had a fully functional, end-to-end application. It wasn't the most feature-rich to-do list app in the world, but it did the one thing it was supposed to do, & it did it well.
Day 4: Showtime!
Day 4 is all about polishing, testing, & deploying. The finish line is in sight!
Morning: Final Testing & Bug Squashing
I spent the morning going through the entire app with a fine-toothed comb. I tried to break it in every way I could think of. I tested it on different browsers, on my phone, & with different user inputs.
I found a few bugs, of course. For example, I discovered that if a user entered a task title that was too long, it would break the UI. I asked Cursor to "add a character limit to the task title input field & display an error message if the user exceeds it." And just like that, the bug was squashed.
Afternoon: Deployment & the Final Touches
It was finally time to deploy. I chose Vercel because it's so easy to use with Next.js. I connected my GitHub repository to Vercel, & with a few clicks, my app was live on the internet.
Of course, it's never that simple, is it? I ran into a last-minute deployment issue. The app was crashing on Vercel, but it was working fine on my local machine. After some frantic debugging (with Cursor's help, of course), I realized the issue was with how I was handling environment variables. I fixed it, pushed the changes, & voila! My SaaS MVP was live.
I also took some time to think about the next steps. As users start signing up, I’ll need a way to engage with them & gather feedback. This is another area where a tool like Arsturn would be incredibly valuable. I could build a chatbot that not only answers questions but also proactively engages with visitors on my website, helping with lead generation & onboarding. Arsturn helps businesses build no-code AI chatbots trained on their own data to boost conversions & provide personalized customer experiences, which is perfect for a lean startup.
So, What's the Verdict?
Building a SaaS MVP in four days was an intense but incredibly rewarding experience. It forced me to be laser-focused on the core value proposition of my product & to be ruthless in cutting out anything that wasn't absolutely essential.
Could I have done it without Cursor? Maybe. But it would have taken me weeks, not days. The ability to generate code from a simple prompt, to get instant feedback on my code, & to have an AI partner to help me debug is a complete game-changer.
This approach isn't just about speed, though. It's about a fundamental shift in how we build software. It's about empowering developers to be more creative & to spend less time on the tedious, repetitive parts of coding.
I hope this diary was helpful. If you have a SaaS idea that's been rattling around in your head, I encourage you to give this a try. You might be surprised at what you can accomplish in just a few days. Let me know what you think