Summary & Key Takeaways ​

• Simon Willison developed "CORS Chat" to test OpenAI-compatible chat endpoints.
• The tool is designed for exercising LLMs like Qwen 3.8 27B in environments such as LM Studio or OpenRouter.
• It provides a web user interface for interacting with these chat services.
• Conversations are automatically persisted within the browser for convenience.
• Users can export their chat history as copy-pasted JSON.
• A unique feature is the progressive rendering of SVG images as they are generated by the LLM.
• The tool successfully integrates with LM Studio using the --cors option and OpenRouter.

Our Commentary ​

I love seeing these kinds of practical, focused tools emerge. Simon Willison just keeps building things that scratch a very specific itch, and this one for testing LLM endpoints is no exception. The progressive SVG rendering is a genuinely cool detail; it's those small UX touches that make a tool feel polished. We've all wrestled with CORS, so a tool that helps streamline testing in that context is always welcome. It's a reminder that even as AI gets more complex, the foundational web challenges persist.