Ladybird browser adopts Rust, ports 25,000 lines of JS engine using Claude Code and Codex

The Ladybird open-source browser project is rewriting parts of its codebase in Rust, starting with LibJS, its JavaScript engine. The 25,000-line port took about two weeks using Claude Code and OpenAI Codex for human-directed translation, with byte-for-byte identical output required from both pipelines. The developer used hundreds of small prompts to steer the agents, followed by adversarial review passes asking different models to analyze the code for mistakes. The port demonstrates AI-assisted language migration at meaningful scale in a real open-source project.

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