CORS Chat

Simon Willison's Blog Tools
cors-chat openai-compatible browser-tool api-testing svg-rendering development-tool

Summary

CORS Chat is a browser-based tool for chatting with OpenAI Responses-compatible API endpoints, featuring custom headers, local conversation saving, and progressive SVG rendering.

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Cached at: 08/16/26, 03:37 AM

# Tool: CORS Chat Source: [https://simonwillison.net/2026/Aug/15/cors-chat/](https://simonwillison.net/2026/Aug/15/cors-chat/) [Tool](https://simonwillison.net/elsewhere/tool/)[CORS Chat](https://tools.simonwillison.net/cors-chat)— Chat directly with any OpenAI Responses\-compatible API endpoint that supports CORS headers, all within your browser\. Configure endpoints with custom headers, save conversations locally, and manage multiple chat sessions with different models and reasoning settings\. I built this today \([with GPT\-5\.6\-Sol xhigh](https://gist.github.com/simonw/92a1d97773744b45bf259e003013cf36)\) to help test Qwen 3\.8 27B running in LM Studio on both my M5 MacBook Pro and an NVIDIA DGX Spark\. It provides a web UI for exercising an OpenAI\-Responses\-compatible chat endpoint\. I've tried it against LM Studio with the`\-\-cors`option and OpenRouter, and both work fine\. Conversations are persisted in the browser and can be exported as copy\-pasted JSON\. One fun detail is that it notices SVG images that are being generated and progressively renders them in the chat while the tokens are still streaming in\. ![Alt text generated by Qwen-3.8 27B: Screenshot of the CORS Chat web interface. The left sidebar lists three saved conversations, with "render an svg of five intersecting squares" selected. The main panel shows a chat with the qwen3.8‑27b model: the user asked "render an svg of five intersecting squares. don't overthink this," followed by the model's reasoning trace describing the design (five semi‑transparent squares rotated around a common center on a dark background). Below is an SVG preview pane displaying five overlapping, semi‑transparent colored squares—pink, blue, green, yellow, and purple—with white outlines, rotated at different angles to form a starburst pattern on a dark navy background. Top controls include endpoint/model selectors and a "New chat" button; the bottom has a message input and a "Send" button.](https://static.simonwillison.net/static/2026/cors-chat.webp)

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