I’ve been closely following the vibe coding trend lately—you know, the whole "describe an app and boom, it’s live in your browser" thing. If you’ve used bolt.new or read my earlier blog about how it works behind the scenes, you know how WebContainers power this magic. They let you run Node.js right in the browser. It’s slick. It’s fast. It feels futuristic.
But then I stumbled upon lovable.dev.
It looked eerily similar—type your idea, get a full-stack app, live preview and all. But when I dug deeper, I realized something wild: Lovable does all of this without using WebContainers.
That had me hooked.
These tools aren’t just side projects anymore. Judging by the ARR trends, companies like Lovable and Bolt are sprinting toward that $100M MRR finish line. But the engineering choices they make under the hood? That’s where it gets interesting.
So, how does Lovable.dev work?
Lovable.dev is one of those tools that feels deceptively simple on the surface. You type an idea into a chat, and minutes later, you’re looking at a live, working app. But under the hood? It’s an orchestration masterpiece.
The frontend is built with React and gives you a smooth chat-style interface. That’s where you describe your app—say, “Build me a recipe tracker using Supabase and TailwindCSS.” Once you submit that prompt, things get interesting.
Behind the scenes, Lovable uses a FastAPI backend that routes your prompt into a multi-layered LLM pipeline. It doesn’t just send your message to a single model. Instead, it first enriches the input—understanding your preferences (frameworks, database, libraries, etc.), and then it breaks the job into stages.
Small models help with planning and defining app features. Think of them as product managers deciding the scope. Then larger models like GPT-4 or Claude take over to write the actual code—frontend, backend, routes, database logic, and even the config files. This division of labor keeps things efficient and scalable.
Once the code is generated, it’s organized into a virtual filesystem—split into the usual suspects:
- Frontend (
/src) - Backend (
/apior/server) package.json.envvariables- Setup instructions for integrations like Supabase or Clerk
Now here’s the kicker: instead of trying to run this entire stack inside your browser (like Bolt.new does with WebContainers), Lovable ships the app to the cloud.
Fly.io + MicroVMs = Real Deployments
Lovable uses Fly.io MicroVMs to host and execute your generated app. These aren’t just containers—they’re lightweight virtual machines built using Firecracker, a virtualization tech developed by AWS (used under the hood by Lambda and Fargate).
So what’s the big deal?
Firecracker-based MicroVMs boot in milliseconds, have super low overhead, and offer strong security isolation. Each app spins up in its own environment—so there’s no cross-app interference, and backend logic, secrets, and integrations all live safely in a cloud-native context.
When you generate an app, Lovable packages up the code—frontend, backend, config files, and any required .env variables—and spins up a new MicroVM on Fly.io. This virtual machine runs the full stack: Node.js, Vite for frontend bundling, API routes, and database connections via Supabase or similar services. Once live, the app is assigned a temporary domain like:
your-project.lovable.app
Then the live preview is piped directly into the Lovable UI via an iframe. What you’re seeing is not a mockup. It’s your actual app, deployed and running in the cloud.
Now here’s something even cooler—Lovable supports live iteration. Whether you tweak the code manually in Dev Mode or ask the AI to add a new feature, the system updates your app on the fly.
- For quick changes like updating styles or editing a React component, Lovable likely uses hot-reloading via the Vite dev server to reflect those changes instantly.
- For heavier edits—like adding a new npm package or modifying backend logic—the platform rebuilds or refreshes the container entirely.
Lovable handles this orchestration seamlessly. So even when a container restart is needed, it ensures the new version is spun up fast, minimizing downtime and keeping your preview in sync with your changes.
To reduce the friction even more, Lovable keeps a pool of pre-warmed MicroVMs ready to go. That means when you trigger a deploy, it doesn’t have to start from zero—the infrastructure is already spun up and waiting.
Lovable vs Bolt.new – The Execution Model Showdown
So let’s compare:
Bolt.new (built by StackBlitz) runs everything in the browser. It uses WebContainers—WASM-powered sandboxes—to emulate Node.js locally. It’s great for fast prototyping and educational use-cases. You get instant reloads, an in-browser terminal, and that sweet local feel. But you’re bound by browser constraints. No real backend. No secure secret handling. No external database like Supabase or Stripe—at least, not cleanly.
Lovable.dev, on the other hand, runs your app in the cloud. Fly.io MicroVMs handle the backend. Secrets are injected securely. You can talk to real APIs, manage databases, and actually deploy full-stack apps. It’s like jumping straight from idea to MVP, no local setup required.
In short:
- Bolt is fast and fun, perfect for learning or frontend-only demos.
- Lovable is heavier, but it’s built for real-world apps.
Final Thoughts
I love how both tools push the boundaries of what’s possible with browser-based development. But what Lovable pulls off without WebContainers? That’s just smart engineering. It proves that you don’t always need to embed everything in the browser. Sometimes, cloud-powered MicroVMs are the better magic trick.
In my experience, Lovable has been far more capable when it comes to generating true full-stack solutions—not just frontend mockups. And what’s even more impressive is how smart it’s getting with UI. Since it leverages React, TailwindCSS, and Shadcn components, I’ve noticed it consistently delivers cleaner, more usable interfaces with less prompting. It genuinely feels like the AI is learning how to design better apps, not just code them.
If you’re curious about building apps with LLMs and deploying them at scale, Lovable is definitely worth exploring.
