AI-integrated development environment (IDE) company Cursor recently implied it had built a working web browser almost entirely with its AI agents. I won't say they lied, but CEO Michael Truell certainly tweeted: "We built a browser with GPT-5.2 in Cursor."

He followed up with: "It's 3M+ lines of code across thousands of files. The rendering engine is from-scratch in Rust with HTML parsing, CSS cascade, layout, text shaping, paint, and a custom JS VM."

That sounds impressive, doesn't it? He also added: "It kind of works," which is not the most ringing endorsement...

Too bad it wasn't true. If you actually looked at Cursor engineer Wilson Lin's blog post about FastRender, the AI-created web browser, you won't see much boasting about a working web browser. Instead, there's a video of a web browser sort of working, and a much less positive note that "building a browser from scratch is extremely difficult."

Developers quickly discovered the "browser" barely compiles, often does not run, and was heavily misrepresented in marketing.

...this week‑long autonomous browser experiment consumed in the order of 10-20 trillion tokens and would have cost several million dollars at then‑current list prices for frontier models.