Simon Willison • 12/16/2025

I ported JustHTML from Python to JavaScript with Codex CLI and GPT-5.2 in 4.5 hours

The article details the process of porting the JustHTML HTML5 parser from Python to JavaScript using AI tools (Codex CLI and GPT-5.2). The author describes the successful creation of a dependency-free JavaScript library that passes over 9,200 tests from the html5lib-tests suite, completing the project in just a few hours with minimal manual intervention.

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#JavaScript #Codex CLI #Gpt 52