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> were the agents working on it able to build it, or were they blindly writing code? The project was able to build the whole time, and the agents were constant

by simonw 10mo ago

> were the agents working on it able to build it, or were they blindly writing code? The project was able to build the whole time, and the agents were constantly compiling it using the Rust compiler and fixing any compile errors as they occurred. The GitHub CI builds were failing, and when they first opened the repo people incorrectly assumed that meant the code didn't compile at all. The biggest problem with the repo when they first released it was that there were no build instructions for end-users, so it was hard to try out. They fixed that within 24 hours of the initial release. > What I don't know, and seemingly nobody else knows, is how functional the rest of the codebase is. It's functional enough to render web pages - you can build it and run it yourself to see that, I have some screenshots from trying it out here: https://simonwillison.net/2026/Jan/19/scaling-long-running-autonomous-coding/ https://simonwillison.net/2026/Jan/19/scaling-long-running-a... That said, it's very much intended as a research project into running parallel coding agents as opposed to a serious browser project that's intended for end users. At the end of my post I compare it to "hello world" - I think "build a browser" may be the "hello world" of massively parallel coding agent systems, which I find quite amusing.

felipeerias 10mo ago
If you were looking for a good long-term AI benchmark, “build me a Web browser” should last you for a while.
beepbooptheory 10mo ago
I hear you but still just struggle what we are supposed to take from this. If I worked for McDonalds and came up with a way to make 1000 bad hamburgers in the time it takes for them to currently make 10 good ones, no one would be that impressed. "Hello world" is self-justifying, you know it when you see it, and it is what it is because it shows something unambiguous and impossible to mistake.
- deleted 10mo ago
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- simonw 10mo ago
  The thing I took from this is that you can arrange a set of coding agents in a tree of planners and workers and have them churn away on much larger projects than if you use a single coding agent. This is a new capability - this likely would now have worked prior to GPT-5.1 and Opus 4.5, so we've had models that can do this for less than three months. It's extremely new: the patterns that work are just starting to be figured out. Wilson had an effectively unlimited token budget from Cursor and got to run experiments that most teams would not be able to afford.
  - polyglotfacto 10mo ago
    The fact that it is new is meaningless: the output is useless even as a proof of concept web engine and should be discarded, alongside the agent engineering pattern that produced it.
    - simonw 10mo ago
      By that logic any experiment that doesn't produce a perfect result should be deleted. I don't think that's a defensible position.
      - polyglotfacto 10mo ago
        Yes, but that is not what I wrote. I wrote: "useless even as a proof of concept". It doesn't have to be perfect; it just needs to show a clear path forward.
        deleted 10mo ago
        [deleted]
        simonw 10mo ago
        I think rendering this is a pretty great proof of concept that illustrates a path forward to doing better: https://static.simonwillison.net/static/2026/cursor-simonwillison.jpg https://static.simonwillison.net/static/2026/cursor-simonwil... If I was trying to build a new browser and I got to that point within a few weeks of starting I would be ecstatic.
polyglotfacto 10mo ago
> it's very much intended as a research project If so then the failure of the experiment should be acknowledged. Failure described among others at: https://news.ycombinator.com/item?id=46705625 https://news.ycombinator.com/item?id=46705625 > It's functional enough to render web pages > FastRender may not be a production-ready browser, but it represents over a million lines of Rust code, written in a few weeks, that can already render real web pages to a usable degree. This is something that can be done in much less than a million lines of code. There must be a core somewhere in Fastrender--probably just a few thousands lines--which is putting together existing layout and graphics libraries and makes it render something to the screen. Doing that in a few weeks isn't impressive, especially not when buried in a million lines of spaghetti code. If you want an example of a real prototype web engine build along radical design choices, head over to https://github.com/DioxusLabs/blitz https://github.com/DioxusLabs/blitz I'm pretty sure it renders far better than Fastrender(the edits the agents made to Taffy are probably nonsense), and I'm guessing it is at most 50k lines. Conclusion: In the light of the efforts to paper over failures, I'm calling Fastrender not a research project but propaganda.
- simonw 10mo ago
  They wanted to figure out patterns to have thousands of agents work on millions of lines together in parallel without stepping on each other's toes. They achieved that. Looks like a success to me. Implementing a browser was just the demo for that. I called it their "hello world" at the end of my post.
  - polyglotfacto 10mo ago
    > Looks like a success to me. How is spaghetti code that does not implement the spec(web standards in this case) success? You are one of the creators of Django; so let me try to give you an analogy: if someone runs thousands of agents in parallel to produce a web framework, and the code ends-up being able to connect to a database and render a template using existing libraries, and the rest would be total non-sense and otherwise useless to web devs; would you call that a success? Success in software requires something that works as intended and is maintainable.

by simonw 10mo ago

felipeerias 10mo ago

If you were looking for a good long-term AI benchmark, “build me a Web browser” should last you for a while.

beepbooptheory 10mo ago

I hear you but still just struggle what we are supposed to take from this. If I worked for McDonalds and came up with a way to make 1000 bad hamburgers in the time it takes for them to currently make 10 good ones, no one would be that impressed. "Hello world" is self-justifying, you know it when you see it, and it is what it is because it shows something unambiguous and impossible to mistake.

deleted 10mo ago
[deleted]
simonw 10mo ago
The thing I took from this is that you can arrange a set of coding agents in a tree of planners and workers and have them churn away on much larger projects than if you use a single coding agent. This is a new capability - this likely would now have worked prior to GPT-5.1 and Opus 4.5, so we've had models that can do this for less than three months. It's extremely new: the patterns that work are just starting to be figured out. Wilson had an effectively unlimited token budget from Cursor and got to run experiments that most teams would not be able to afford.
- polyglotfacto 10mo ago
  The fact that it is new is meaningless: the output is useless even as a proof of concept web engine and should be discarded, alongside the agent engineering pattern that produced it.
  - simonw 10mo ago
    By that logic any experiment that doesn't produce a perfect result should be deleted. I don't think that's a defensible position.
    - polyglotfacto 10mo ago
      Yes, but that is not what I wrote. I wrote: "useless even as a proof of concept". It doesn't have to be perfect; it just needs to show a clear path forward.
      - deleted 10mo ago
        [deleted]
      - simonw 10mo ago
        I think rendering this is a pretty great proof of concept that illustrates a path forward to doing better: https://static.simonwillison.net/static/2026/cursor-simonwillison.jpg https://static.simonwillison.net/static/2026/cursor-simonwil... If I was trying to build a new browser and I got to that point within a few weeks of starting I would be ecstatic.

polyglotfacto 10mo ago

> it's very much intended as a research project If so then the failure of the experiment should be acknowledged. Failure described among others at: https://news.ycombinator.com/item?id=46705625 https://news.ycombinator.com/item?id=46705625 > It's functional enough to render web pages > FastRender may not be a production-ready browser, but it represents over a million lines of Rust code, written in a few weeks, that can already render real web pages to a usable degree. This is something that can be done in much less than a million lines of code. There must be a core somewhere in Fastrender--probably just a few thousands lines--which is putting together existing layout and graphics libraries and makes it render something to the screen. Doing that in a few weeks isn't impressive, especially not when buried in a million lines of spaghetti code. If you want an example of a real prototype web engine build along radical design choices, head over to https://github.com/DioxusLabs/blitz https://github.com/DioxusLabs/blitz I'm pretty sure it renders far better than Fastrender(the edits the agents made to Taffy are probably nonsense), and I'm guessing it is at most 50k lines. Conclusion: In the light of the efforts to paper over failures, I'm calling Fastrender not a research project but propaganda.

simonw 10mo ago
They wanted to figure out patterns to have thousands of agents work on millions of lines together in parallel without stepping on each other's toes. They achieved that. Looks like a success to me. Implementing a browser was just the demo for that. I called it their "hello world" at the end of my post.
- polyglotfacto 10mo ago
  > Looks like a success to me. How is spaghetti code that does not implement the spec(web standards in this case) success? You are one of the creators of Django; so let me try to give you an analogy: if someone runs thousands of agents in parallel to produce a web framework, and the code ends-up being able to connect to a database and render a template using existing libraries, and the rest would be total non-sense and otherwise useless to web devs; would you call that a success? Success in software requires something that works as intended and is maintainable.