Cursor CEO Built a Browser with AI: Does It Work?

The landscape of software development is shifting beneath our feet. Just a few years ago, we were amazed when an AI could auto-complete a function. Today, we are witnessing AI agents architecting entire systems.

Recently, Michael Truell, the CEO of Cursor, made headlines with a staggering experiment: he and his team used hundreds of AI agents to build a functional web browser from scratch in just one week. The project, dubbed "FastRender," generated over 3 million lines of code.

As a developer who works daily with Generative AI to build solutions for clients, I found this experiment fascinating—not just for what was built, but for how it was built. But the big question remains: Does it actually work, and what does this mean for the rest of us?

The Experiment: FastRender

Building a web browser is notoriously difficult. It requires handling complex specifications for HTML parsing, CSS cascading, layout engines, and JavaScript execution. It's a task usually reserved for massive teams at Google, Apple, or Mozilla over spans of years.

Truell’s experiment leveraged GPT-5.2 powered agents working continuously. The result was a browser engine written primarily in Rust, featuring:

A custom Rendering Engine: Handling painting and text shaping.
HTML & CSS Parsers: Built from scratch.
A JavaScript Virtual Machine: Custom implementation.

This wasn't just a wrapper around an existing webview; it was a fundamental reconstruction of browser technology.

But... Does It Actually Work?

The short answer is: Yes, but with caveats.

Truell himself admitted that FastRender "kind of works." It can render simple websites quickly and correctly, which is a massive achievement for a week's worth of automated work. However, it falls short of the mature, battle-tested stability of Chromium or WebKit. It struggles with the complex, dynamic interactivity of modern web applications.

If you were hoping to switch from Chrome to an AI-generated browser tomorrow, you'd be disappointed. But judging it by that metric misses the point entirely.

The Real Breakthrough: Agentic Coordination

The true significance of FastRender isn't the browser itself; it's the successful coordination of AI agents at scale.

We are moving past the era of the "AI Copilot"—where the AI helps you write the next few lines of code—into the era of the "AI Coworker" or "AI Squad." In this experiment, agents didn't just write code; they managed dependencies, adhered to architectural patterns, and contributed to a cohesive codebase spanning thousands of files.

This signals a change in the developer's role. We are transitioning from translators (converting thoughts to syntax) to architects and reviewers (defining goals and verifying system integrity).

What This Means for Developers

For Shopify merchants, app developers, and tech founders, this evolution offers a glimpse into a future where the barrier to entry for complex software is drastically lowered.

Rapid Prototyping: We can now envision building "impossible" MVPs in days rather than months.
Legacy Modernization: AI agents could theoretically be deployed to refactor massive legacy codebases that humans are too afraid to touch.
Higher Level Thinking: Developers must focus more on system design, security, and user experience. If the AI writes the boilerplate, your value lies in the strategy.

Conclusion

Cursor's browser experiment is a proof of concept for the future of engineering. While the browser itself might not replace Chrome today, the methodology used to build it will undoubtedly replace how we build software tomorrow.

The best time to start integrating AI into your workflow was yesterday. The second best time is today. Whether you're building a Shopify app or a custom platform, understanding how to orchestrate AI tools is rapidly becoming the most valuable skill in our industry.