How to Build a SaaS with AI (Modern Stack)

The modern SaaS stack in one picture

A SaaS is the same three layers as any app (a frontend the user sees, a backend that holds logic and secrets, and a database that stores data) plus the few services that turn an app into a business: authentication so users have accounts, a database that syncs in real time, and payments so you can charge. The 2026 default for a solo founder or small team is a framework for the app, Clerk for auth, Convex for the reactive database, and Stripe for payments, all glued together by a coding agent you direct. You do not have to use these exact tools, but you do need one good choice in each slot. Our cornerstone article, Modern App Stack Explained, lays out the full picture; this guide is the build path through it.

• App framework: renders the UI and serves the app (Next.js, TanStack Start, Astro and others).
• Auth: user accounts, login and OAuth, handled by a provider so you never store passwords yourself.
• Database: where your data lives and syncs; Convex is reactive so the UI updates live.
• Payments: Stripe for checkout, subscriptions and webhooks. See the article Modern App Stack Explained for the whole map.

Step 1: idea to scaffold

Start by narrowing the idea to one job your product does well, then let your agent scaffold the project. The discipline that matters here is scope: a SaaS that does one thing clearly beats one that does ten things vaguely, exactly as the favicon-maker build learned. Have your coding agent set up the framework, version control and a dev server, and get a blank app running locally before you add anything. Write a CLAUDE.md with your stack and conventions so the agent builds on your rules from the first commit. The goal of this stage is a running skeleton you can deploy, not a feature, because shipping the empty shell early de-risks everything that follows.

• Narrow to one core job; resist feature creep before you have shipped anything.
• Let the agent scaffold the framework, Git and a dev server, and run it locally.
• Add a CLAUDE.md so the agent follows your stack and conventions from the start.
• Course 3 lesson: Architecture 101 explains how the pieces fit before you wire them.

Step 2: add authentication with Clerk

Almost every SaaS needs accounts, and you should never build login from scratch: rolling your own auth is how secrets leak and sessions break. An auth provider handles signup, login, OAuth (sign in with Google and others), sessions and security for you, so you wire in a few components and protect your routes. Clerk is the default we teach because it is fast to integrate and pairs cleanly with this stack, but Auth0 and Supabase Auth are valid choices depending on your needs. We break down that decision in the Clerk vs Auth0 vs Supabase Auth comparison; whichever you pick, the principle is the same: delegate the security-critical part to specialists. The Modern App Stack course walks the full Clerk integration including Google OAuth and the dev-to-production move.

• Never roll your own auth; a provider handles login, OAuth, sessions and security.
• Clerk is the default here; weigh it against Auth0 and Supabase Auth in our comparison.
• Wire in the auth components, then protect the routes and data that need a signed-in user.
• Course 3 lesson: Clerk authentication and OAuth from dev to production.

Step 3: model your data in Convex

Your SaaS needs somewhere to store data that survives a refresh and is shared across users, and the modern choice for this stack is Convex: a reactive database where your queries update the UI automatically when the underlying data changes, so you write far less synchronisation code. You define your schema, write functions that read and write data, and the frontend subscribes to live results. Convex is not the only option (Supabase and Firebase are strong alternatives with different trade-offs), and we lay that decision out in the Convex vs Supabase vs Firebase comparison. The reason reactive data matters for a solo founder is leverage: the database doing the live updates for you is one less system you have to build and debug. The Modern App Stack course covers modelling data and writing Convex functions in full.

• A database stores data permanently and shares it across users and sessions.
• Convex is reactive: queries update the UI live, so you write less sync code.
• Compare it against Supabase and Firebase in our backend comparison before you commit.
• Course 3 lesson: Convex, your reactive database. Design the API and schema before the UI, as the BizCollect build learned.

Step 4: charge customers with Stripe

A SaaS is a business, so it needs payments, and Stripe is the standard for checkout, subscriptions and the webhooks that keep your app in sync with what a customer actually paid. The flow has two halves. First, checkout and subscriptions: you create products and prices, send the customer to Stripe to pay, and bring them back. Second, the webhooks: Stripe tells your backend when a payment succeeds, a subscription renews or a card fails, and your code updates the user record accordingly. The trap beginners hit is treating the redirect as the source of truth; the webhook is. Always handle secrets safely and keep your Stripe keys out of frontend code and out of Git. The Modern App Stack course covers Stripe in two lessons: checkout and subscriptions, then webhooks, proration and coupons.

• Stripe handles checkout, subscriptions and the billing edge cases you should not build yourself.
• Webhooks, not the redirect, are the source of truth for what a customer paid.
• Keep Stripe secret keys in the backend and out of version control.
• Course 3 lessons: Stripe Part 1 (checkout, subscriptions) and Stripe Part 2 (webhooks, proration, coupons).

Step 5: ship it

The last stage is the one beginners put off and should do early: getting the app from your machine to the public internet, in production, with real keys. That means moving each service (auth, database, payments) from its development mode to production, handling environment variables and secrets correctly, setting up your domain, and submitting the site to Search Console so it can be found. Shipping is not a one-time event at the end; it is a loop you should run from the empty scaffold onward, so going live is boring rather than terrifying. The Modern App Stack course closes with exactly this: the dev-to-production migration, Search Console and performance. Once it is live, you direct the agent to add features the same way you built the skeleton, verifying each change before it ships.

• Move auth, database and payments from development to production mode with real keys.
• Handle secrets and environment variables correctly; never commit keys.
• Set up your domain and submit the site to Search Console so it gets found.
• Course 3 lesson: Going live, the dev-to-prod migration, Search Console and performance.

Direct the agent, do not just vibe it

Building a SaaS with AI is the clearest case for agentic engineering over vibe coding. A weekend prototype can be vibed, but a product with real users, their data and their money cannot: a silent bug in your Stripe webhook or an unprotected Convex query is the kind of mistake that costs trust or cash. So you direct the agent and verify its work: plan before it edits, read the diffs on anything touching auth, data or payments, and keep a quality gate (lint, types, tests) green. The same agents that produce a fragile pile when you accept everything unchecked produce a maintainable SaaS when you stay the engineer of record. Real products are built this way; the CallAssistant build is a working SaaS shipped on this exact discipline, and the What Is Agentic Engineering pillar explains the mindset in full.

• Vibe a prototype; direct and verify anything with real users, data or payments.
• Plan before editing and read every diff that touches auth, data or money.
• Keep a quality gate green so a regression cannot slip into production.
• See the CallAssistant build for a shipped SaaS and the What Is Agentic Engineering pillar for the discipline.

Step by step

1. 01

   Scaffold the project

   Narrow the idea to one core job, then have your coding agent set up the framework, Git and a dev server. Add a CLAUDE.md with your stack and conventions, and get a blank app running locally.

2. 02

   Add authentication

   Wire in an auth provider (Clerk by default) for signup, login and OAuth, and protect the routes and data that require a signed-in user. Never build login from scratch.

3. 03

   Model your data

   Define your schema and write read and write functions in a reactive database like Convex, so the frontend subscribes to live results. Design the data shape before the UI.

4. 04

   Add payments

   Set up Stripe products and prices, add checkout and subscriptions, and handle webhooks as the source of truth for what a customer paid. Keep secret keys in the backend.

5. 05

   Ship to production

   Move auth, database and payments to production mode with real keys, handle secrets correctly, connect your domain, and submit the site to Search Console.

6. 06

   Iterate by directing the agent

   Add features the way you built the skeleton: plan before editing, read the diffs on anything touching auth, data or payments, and keep your quality gate green before each ship.

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