I'm eager to find out if this was actually successfully compiled at one point (otherwise how did they get the screenshots?), so I'm running `cargo check` for each of the last 100 commits to see if anything works. Will update here with the results once it's ready.
Key phrase "They never actually claim this browser is working and functional
" This is what most AI "successes" turn out to be when you apply even a modicum of scrutiny.
I wonder who they actually tried to impress with that? People who understand and appreciate the difficulty of building a browser from scratch would surely be interested to understand what you (or your Agent) did to a degree that they would understand if you didn’t.
The blog[0] is worded rather conservatively but on Twitter [2] the claim is pretty obvious and the hype effect is achieved [2]
CEO stated "We built a browser with GPT-5.2 in Cursor"
instead of
"by dividing agents into planners and workers we managed to get them busy for weeks creating thousands of commits to the main branch, resolving merge conflicts along the way. The repo is 1M+ lines of code but the code does not work (yet)"
This is why AI skeptics exist. We’re now at the point where you can make entirely unsubstantiated claims about AI capability, and even many folks on HN will accept it with a complete lack of discernment. The hype is out of control.
I think the original post was just headline bait. There is such a fast news cycle around AI that many people would take "Thousands of AI agents collaborate to make a web browser" at face value.
A fast news cycle around projects that don't actually work. It's a real bummer that "fake news" became politically charged because it's a perfect description of this segment.
> 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.
"From scratch" sounds very impressive. "custom JS VM" is as well. So let's take a look at the dependencies [1], where we find
- html5ever
- cssparser
- rquickjs
That's just servo [2], a Rust based browser initially built by Mozilla (and now maintained by Igalia [3]) but with extra steps. So this supposed "from scratch" browser is just calling out to code written by humans. And after all that it doesn't even compile! It's just plain slop.
To be fair, even if "from scratch" means "download and build Chromium", that's still nontrivial to accomplish. And with how complicated a modern browser is, you can get into Ship of Theseus philosophy pretty fast.
I wouldn't particularly care what code the agents copied, the bigger indictment is the code doesn't work.
So really, they failed to meet the bar of "download and build Chromium" and there's no point to talk about the code at all.
> The JS engine used a custom JS VM being developed in vendor/ecma-rs as part of the browser, which is a copy of my personal JS parser project vendored to make it easier to commit to.
Why would they think it's a great idea to claim they implemented CSS and JS from scratch when the first thing any programmer would do is to look at the code and immediately find out that they're just using libraries for all of that?! They can't be as dumb as thinking no one would've noticed?!
I guess the answer is that most people will see the claim, read a couple of comments about "how AI can now write browsers, and probably anything else" from people who are happy to take anything at face value if it supports their view (or business) and move on without seeing any of the later comotion. This happens all the time with the news. No one bothers to check later if claims were true, they may live their whole lives believing things that later got disproved.
I'm reminded of the viral tweet along the lines of "Claude just one-shotted a 10k LOC web app from scratch, 10+ independent modules and full test coverage. None of it works, but it was beautiful nonetheless."
Thanks for the feedback. I've addressed similar feedback at [0] and provided some more context at [1].
I do want to briefly note that the JS VM is custom and not QuickJS. It also implemented subsystems like the DOM, CSS cascade, inline/block/table layouts, paint systems, text pipeline, and chrome, and I'd push back against the assertion that it merely calls out to external code. I addressed these points in more detail at [0].
The Actions overview is impressive: There have been 160,469 workflow runs, of which 247 succeeded. The reason the workflows are failing is because they have exceeded their spending limit. Of course, the agents couldn't care less.
IMHO people are missing the forest for the trees. The point of this experiment is not to build a functional browser but to develop ways to make agents create large codebases from scratch over a very long time span. A Web browser is just a convenient target because there are lots of documentation, specs and tests available.
I actually ran this one. It measures some 700k lines of code, and seems to contain things like a full VBA implementation, complex currency and date parsing, etc. But the UI is extremely basic, doesn't seem to expose any of this advanced functionality, and and is buggy to the point of being unusable. Focus will jump around as you type, cells will reset to old values, it will stop responding to keyboard events, etc.
In all sincerity, this question is almost identical to "what's the most difficult thing about building an operating system" as a modern browser is tens of millions of lines of code that can run sophisticated applications. It has a network stack, half a dozen parsers, frame construction and reflow modules, composite, render and paint components, front end UI components, an extensibility framework, and more. Each one of these must enable supporting backward compatibility for 30 year old content as well as ridiculously complex contemporary web apps. And it has to load and render sites that a completely programming illiterate fool like me wrote. It must do this all in a performant and secure way using minimal system resources. Also, it probably also must run on Mac, Windows, Linux, Android, iOS, and maybe more.
Check out the list of all CSS specifications [1], and then open any one of them and see how lengthy and elaborate each is. Then do the same for each version of the spec published over the last thirty years. Before you can start, you must read and understand all of this at a great level of depth. Still, specifications never tell the complete story. You must be aware of all the nuances that are implied by each requirement in the spec and know how to handle the zillion corner cases that will crop up inevitably.
And this is just one part. Not even considering the fully sandboxed, mini operating system for running webapps.
I haven’t studied the project that this is a comment on, but: The article notices that something that compiles, runs, and renders a trivial HTML page might be a good starting point, and I would certainly agree with that when it’s humans writing the code. But is it the only way? Instead of maintaining “builds and runs” as a constant and varying what it does, can it make sense to have “a decent-sized subset of browser functionality” as a constant and varying the “builds and runs” bit? (Admittedly, that bit does not seem to be converging here, but I’m curious in more general terms.)
Always take any pronouncement from an AI company (heavily dependent on VC and public sentiment on AI) with a heavy grain of salt..
hype over reality
I’m building an AI startup myself and I know that world and its full of hypsters and hucksters unfortunately - also social media communication + low attention span + AI slop communication is a blight upon todays engineering culture
I am not an expert AI user, but one typical 'failure mode' I see constantly is the AI reimplementing features that already exist in the codebase, or breaking existing ones.
> company claims they "built a browser" from scratch
> looks inside
> completely useless and busted
30 billion dollar VS Code fork everyone. When we do start looking at these people for what they are: snake oil salesmen.
They slop laundered the FOSS Servo code into a broken mess and called it a browser, but dumbasses with money will make line go up based on lies. EFF right off.
I recently was convinced by colleagues to try Cursor at work for project planning. At first I was excited for something even better than Copilot Chat, but then I quickly realized it's just a shitty VS Code fork with maybe a few improvements that are by no means a moat for that company. Worse yet, it makes lots of bizarre mistakes, deletes lines for no good reason, and sometimes even deletes the entire project plan. The scroll on the chat history gets laggy very quickly, and I've found the whole program to be glitchy as hell.
The hype around Cursor is unreal. My suspicion is this company is little more than a parasite with no qualms about getting you to waste your tokens. It's one thing when a product is new, but Cursor has been around since 2023 I guess? The quality of their software is unacceptable.
The comment that points out that this week-long experiment produced nothing more than a non-functional wrapper for Servo (an existing Rust browser) should be at the top:
I really doubt this marketing approach is effective. Isn't this just shooting themselves in the foot? My actual experience with Cursor has been: their design is excellent and the UX is great—it handles frontend work reasonably well. But as soon as you go deeper, it becomes very prone to serious bugs. While the addition of Claude's new models has helped somewhat, the results are still not as good as Google's Antigravity (despite its poor UX and numerous bugs). What's worse, even with this much-hyped Claude model, you can easily blow through the $20 subscription limit in just a few days. Maybe they're betting on models becoming 10x better and 10x cheaper, but that seems unlikely to happen anytime soon.
The amount of negativity in the original post was astounding.
People were making all sorts of statements like:
- “I cloned it and there were loads of compiler warnings”
- “the commit build success rate was a joke”
- “it used 3rd party libs”
- “it is AI slop”
What they all seem to be just glossing over is how the project unfolded: without human intervention, using computers, in an exceptionally accelerated time frame, working 24hr/day.
If you are hung up on commit build quality, or code quality, you are completely missing the point, and I fear for your job prospects. These things will get better; they will get safer as the workflows get tuned; they will scale well beyond any of us.
Don’t look at where the tech is. Look where it’s going.
Like it or not, it's a fundraising strategy. They have followed it mutliple times (eg: vague posts about how much their inhouse model is writing code, online RL, and lines of code etc. earlier) and it was less vague before. They released a model and did not give us the exact benchmarks or even tell us the base model for the same. This is not to imply there is no substance behind it, but they are not as public about their findings as one would like them to be. Not a criticism, just an observation.
69 comments
[ 173 ms ] story [ 2019 ms ] threadEdit: As mentioned, I ran `cargo check` on all the last 100 commits, and seems every single of them failed in some way: https://gist.github.com/embedding-shapes/f5d096dd10be44ff82b...
Their AI is probably better at producing images than writing code
investors?
CEO stated "We built a browser with GPT-5.2 in Cursor"
instead of
"by dividing agents into planners and workers we managed to get them busy for weeks creating thousands of commits to the main branch, resolving merge conflicts along the way. The repo is 1M+ lines of code but the code does not work (yet)"
[0] https://cursor.com/blog/scaling-agents
[1] https://x.com/kimmonismus/status/2011776630440558799
[2] https://x.com/mntruell/status/2011562190286045552
[3]https://www.reddit.com/r/singularity/comments/1qd541a/ceo_of...
> 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.
"From scratch" sounds very impressive. "custom JS VM" is as well. So let's take a look at the dependencies [1], where we find
- html5ever
- cssparser
- rquickjs
That's just servo [2], a Rust based browser initially built by Mozilla (and now maintained by Igalia [3]) but with extra steps. So this supposed "from scratch" browser is just calling out to code written by humans. And after all that it doesn't even compile! It's just plain slop.
[1] - https://github.com/wilsonzlin/fastrender/blob/main/Cargo.tom...
[2] - https://github.com/servo/servo
[3] - https://blogs.igalia.com/mrego/servo-2025-stats/
I wouldn't particularly care what code the agents copied, the bigger indictment is the code doesn't work.
So really, they failed to meet the bar of "download and build Chromium" and there's no point to talk about the code at all.
https://news.ycombinator.com/item?id=46650998
We at least it's not outright ripping them off like it usually does.
I guess the answer is that most people will see the claim, read a couple of comments about "how AI can now write browsers, and probably anything else" from people who are happy to take anything at face value if it supports their view (or business) and move on without seeing any of the later comotion. This happens all the time with the news. No one bothers to check later if claims were true, they may live their whole lives believing things that later got disproved.
That, or they have some incentive to lie about it.
I'm not sure which one of these is false (if any)
I do want to briefly note that the JS VM is custom and not QuickJS. It also implemented subsystems like the DOM, CSS cascade, inline/block/table layouts, paint systems, text pipeline, and chrome, and I'd push back against the assertion that it merely calls out to external code. I addressed these points in more detail at [0].
[0] https://news.ycombinator.com/item?id=46650998 [1] https://news.ycombinator.com/item?id=46655608
https://github.com/wilson-anysphere/formula
The Actions overview is impressive: There have been 160,469 workflow runs, of which 247 succeeded. The reason the workflows are failing is because they have exceeded their spending limit. Of course, the agents couldn't care less.
And this is just one part. Not even considering the fully sandboxed, mini operating system for running webapps.
[1] https://www.w3.org/Style/CSS/specs.en.html
I mean by definition something that doesn't build and run doesn't have any browser-like functionality at all.
Always take any pronouncement from an AI company (heavily dependent on VC and public sentiment on AI) with a heavy grain of salt..
hype over reality
I’m building an AI startup myself and I know that world and its full of hypsters and hucksters unfortunately - also social media communication + low attention span + AI slop communication is a blight upon todays engineering culture
I couldn’t make it render the apple page that was on the Cursor promo. Maybe they’ve used some other build.
> looks inside
> completely useless and busted
30 billion dollar VS Code fork everyone. When we do start looking at these people for what they are: snake oil salesmen.
They slop laundered the FOSS Servo code into a broken mess and called it a browser, but dumbasses with money will make line go up based on lies. EFF right off.
The hype around Cursor is unreal. My suspicion is this company is little more than a parasite with no qualms about getting you to waste your tokens. It's one thing when a product is new, but Cursor has been around since 2023 I guess? The quality of their software is unacceptable.
https://news.ycombinator.com/item?id=46649046
People were making all sorts of statements like: - “I cloned it and there were loads of compiler warnings” - “the commit build success rate was a joke” - “it used 3rd party libs” - “it is AI slop”
What they all seem to be just glossing over is how the project unfolded: without human intervention, using computers, in an exceptionally accelerated time frame, working 24hr/day.
If you are hung up on commit build quality, or code quality, you are completely missing the point, and I fear for your job prospects. These things will get better; they will get safer as the workflows get tuned; they will scale well beyond any of us.
Don’t look at where the tech is. Look where it’s going.