Go to Customize → Connectors, click + Add, then Add custom connector.
Name it ZIP Codes and paste this server URL:
https://mcp.zip-codes.com/mcp
Choose No sign in, then add it.
Start a new chat, click + and turn on ZIP Codes.
The free plan allows one custom connector. Once it's added on the web, it also works in the Claude desktop and phone apps.
In a web browser, open chatgpt.com/plugins and sign in. Click +, then Add custom MCP server.
Name it ZIP Codes and paste this server URL:
https://mcp.zip-codes.com/mcp
Choose No authentication, then create it as a plugin.
Install the plugin and accept the warning.
Start a new chat and type @ZIP Codes before your question.
Custom servers need a paid ChatGPT plan, and ChatGPT changes these menus often. If yours look different, see our setup page.
Now ask your assistant:
“What county is ZIP Code 60601 in, which area codes does it use, and what is its median household income?”
This sample answers in full without a key. For other places, some details come back as asterisks: those need a free API key, which you can add later (see our setup page).