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Codex CLI is OpenAI’s agentic coding assistant. It reads MCP server definitions from a YAML config file.

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File location

~/.codex/config.yaml
Create the file if it doesn’t exist.

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Config

mcp_servers:
  versuno:
    command: npx
    args: ["-y", "versuno-mcp"]
    env:
      VERSUNO_API_KEY: uk_live_xxx

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Enabling the server

Restart Codex CLI after saving the config. On the next run, Codex will spawn the versuno-mcp process automatically. You can confirm it loaded by running: 
codex --list-tools
You should see the Versuno tools in the output: the brain tools (list_public_brains, query_brain, get_brain_tree, get_brain_node) and the prompt manager tools (list_assets, search_assets, get_asset, pull_asset, push_asset).

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Project-scoped config

To restrict the server to a single project, add a codex.yaml to your project root with the same mcp_servers block. Project config takes precedence over the global config.

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Using it

Start a session and reference your assets naturally:
“Pull the ‘API context’ asset from Versuno and use it as background for this task.”
Codex asks for approval before each MCP tool call. Keep this enabled. See Security.

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Troubleshooting

Run Codex with verbose output to see MCP stderr: 
codex --verbose
The most common issues are a missing or invalid API key. See Troubleshooting.