Adding a custom MCP server to Claude and ChatGPT

Simon Willison documented how to connect a custom MCP server to the web chat UIs of Claude and ChatGPT, revealing that the process requires multiple steps despite both platforms supporting MCP access. The guide, published on 29th July 2026, provides practical instructions for developers exploring the Model Context Protocol.

29th July 2026 TIL /elsewhere/til/ Adding a custom MCP server to Claude and ChatGPT https://til.simonwillison.net/llms/mcp-in-claude-and-chatgpt — I've started exploring MCP https://modelcontextprotocol.io/ in more detail. The web chat UIs for both Claude and ChatGPT can access MCP servers but it's not obvious how to set them up. Here's what I figured out. Connecting a custom MCP server to Claude and ChatGPT's standard chat interfaces is possible, but can take quite a few steps. Recent articles OpenAI’s accidental cyberattack against Hugging Face is science fiction that happened /2026/Jul/22/openai-cyberattack/ - 22nd July 2026 A Fireside Chat with Cat and Thariq from the Claude Code team /2026/Jul/21/cat-and-thariq/ - 21st July 2026 Kimi K3, and what we can still learn from the pelican benchmark /2026/Jul/16/kimi-k3/ - 16th July 2026