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Connect OpenAI Codex

OpenAI's MCP-speaking CLI. Same MCP server as Cursor + Claude — different config file.

OpenAI's Codex CLI is MCP-native as of v0.5+. Add Nomos as one of its MCP servers and your Codex agent gets the same policy gate as every other Nomos-connected agent.

Before you start

  • Codex CLI 0.5+ (`npm i -g @openai/codex`).
  • A Nomos App with an API key.
  • At least one Connection.

Config location

Codex reads ~/.codex/config.toml (macOS / Linux) or %APPDATA%\codex\config.toml (Windows).

The block to add

toml
[mcp_servers.nomos]
command = "npx"
args = ["-y", "@auto-nomos/mcp-server@latest"]

[mcp_servers.nomos.env]
NOMOS_CONTROL_URL = "https://control.auto-nomos.com"
NOMOS_API_KEY = "nk_live_…"
NOMOS_PDP_URL = "https://pdp.auto-nomos.com"

Append this to your existing config.toml — don't replace the file.

config.toml open with the Nomos block highlighted
TOML, not JSON. Indent the env table under the server's namespace.

Run Codex

bash
codex "open a PR on acme/app that bumps the README copyright year"

Codex picks github_pr_create, the MCP server asks Nomos, the PDP runs your policy. If the policy allows the command outright, you get the PR. If the policy requires step-up (because PR creation is a write), Codex pauses while you approve on your phone, then continues.

Codex CLI showing a github_pr_create call with approval pending
Codex pauses at the step-up gate. Once you approve, it continues with the cosigner UCAN.

Common failures

  • Codex doesn't see Nomos tools+
    Codex caches MCP servers for 60s. `codex mcp refresh` forces a re-discovery. Or restart the session.
  • TOML parse error on launch+
    Codex is strict about TOML. Make sure the env values are bare strings (NOMOS_API_KEY = "nk_live_…"), not arrays or tables.
  • Want one Codex per project+
    Codex respects a project-local config at `.codex/config.toml`. Drop the same block there; the project config layers on top of the global one.
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