When AI 'builds a browser,' check the repo before believing the hype

Summary

Opinion 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. Still, numerous news sources and social media chatterboxes ran with the news that AI built a web browser in a week. 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." The thing about making such a software announcement on GitHub is that while the headlines are proclaiming another AI victory, developers have this nasty trick. They actually git the code and try it out. Developers quickly discovered the "browser" barely compiles, often does not run, and was heavily misrepresented in marketing. As a techie, the actual blog post about how they tried and didn't really succeed was much more interesting. Of course, that Cursor sicced hundreds of GPT-5.2-style agents which ran for a week to produce three million lines of new code, to produce, at best, a semi-functional web browser from scratch, doesn't make for a good headline. According to Perplexity, my AI chatbot of choice, 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. I'd just cloned a copy of Chromium myself, and for all that t...