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I wrote JustHTML using coding agents

14 points by simonw

by minusf

1 subcomments

while it's mentioned in the post, it seems to me a bit burried:
isn't this more like a port of `html5ever` from rust to python using LLM, as opposed to creating something "new" based on the test suite alone?
if yes, wouldn't be the distinction rather important?

by simonw

2 subcomments

JustHTML https://github.com/EmilStenstrom/justhtml is a neat new Python library - it implements a compliant HTML5 parser in ~3,000 lines of code that passes the full existing 9,200 test HTML5 conformance suite.
Emil Stenström wrote it with a variety of coding agent tools over the course of a couple of months. It's a really interesting case study in using coding agents to take on a very challenging project, taking advantage of their ability to iterate against existing tests.
I wrote a bit more about it here: https://simonwillison.net/2025/Dec/14/justhtml/