Advanced

Non-interactive / CI mode

Run Codex head-less in pipelines. Example GitHub Action step:

- name: Update changelog via Codex
  run: |
    npm install -g @openai/codex
    export OPENAI_API_KEY="${{ secrets.OPENAI_KEY }}"
    codex exec --full-auto "update CHANGELOG for next release"

Tracing / verbose logging

Because Codex is written in Rust, it honors the RUST_LOG environment variable to configure its logging behavior.

The TUI defaults to RUST_LOG=codex_core=info,codex_tui=info and log messages are written to ~/.codex/log/codex-tui.log, so you can leave the following running in a separate terminal to monitor log messages as they are written:

tail -F ~/.codex/log/codex-tui.log

By comparison, the non-interactive mode (codex exec) defaults to RUST_LOG=error, but messages are printed inline, so there is no need to monitor a separate file.

See the Rust documentation on RUST_LOG for more information on the configuration options.

Model Context Protocol (MCP)

The Codex CLI can be configured to leverage MCP servers by defining an mcp_servers section in ~/.codex/config.toml. It is intended to mirror how tools such as Claude and Cursor define mcpServers in their respective JSON config files, though the Codex format is slightly different since it uses TOML rather than JSON, e.g.:

# IMPORTANT: the top-level key is `mcp_servers` rather than `mcpServers`.
[mcp_servers.server-name]
command = "npx"
args = ["-y", "mcp-server"]
env = { "API_KEY" = "value" }

TIP

It is somewhat experimental, but the Codex CLI can also be run as an MCP server via codex mcp. If you launch it with an MCP client such as npx @modelcontextprotocol/inspector codex mcp and send it a tools/list request, you will see that there is only one tool, codex, that accepts a grab-bag of inputs, including a catch-all config map for anything you might want to override. Feel free to play around with it and provide feedback via GitHub issues.