Install Cairn in Codex

What you need first

• Codex, installed.
• Docker, which gives the docker command the server starts with.
• Your own values for YOUR_CAIRN_DB_HOST,YOUR_CAIRN_DB_PASS.

Steps

1. Run this in a terminal. It writes the server into ~/.codex/config.toml, which the Codex CLI, its IDE extension and the ChatGPT desktop app share.

codex mcp add cairn-mcp --env CAIRN_DB_HOST=YOUR_CAIRN_DB_HOST --env CAIRN_DB_PASS=YOUR_CAIRN_DB_PASS -- docker run -i --rm -e CAIRN_DB_HOST -e CAIRN_DB_PASS ghcr.io/jasondostal/cairn-mcp:0.21.2

2. Replace YOUR_CAIRN_DB_HOST,YOUR_CAIRN_DB_PASS with your own values.
3. Start Codex again and type /mcp: the server is listed.

Check it worked

Ask Codex: List the tools of cairn-mcp.

If it does not start

Cannot connect to the Docker daemon

Docker is not running. Start it, then restart Codex.

The server starts, but its tools fail

A YOUR_… placeholder is still in the config, or its value is wrong.