Advanced

If you already lean on Codex every day and just need a little more control, this page collects the knobs you are most likely to reach for: tweak defaults in Config, add extra tools through Model Context Protocol support, and script full runs with codex exec. Jump to the section you need and keep building.

Config quickstart

Most day-to-day tuning lives in config.toml: set approval + sandbox presets, pin model defaults, and add MCP server launchers. The Config guide walks through every option and provides copy-paste examples for common setups.

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,codex_rmcp_client=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 and IDE extension is a MCP client which means that it can be configured to connect to MCP servers. For more information, refer to the config docs.

Using Codex as an MCP Server

The Codex CLI can also be run as an MCP server via codex mcp-server. For example, you can use codex mcp-server to make Codex available as a tool inside of a multi-agent framework like the OpenAI Agents SDK. Use codex mcp separately to add/list/get/remove MCP server launchers in your configuration.

Codex MCP Server Quickstart

You can launch a Codex MCP server with the Model Context Protocol Inspector:

npx @modelcontextprotocol/inspector codex mcp-server

Send a tools/list request and you will see that there are two tools available:

codex - Run a Codex session. Accepts configuration parameters matching the Codex Config struct. The codex tool takes the following properties:

Property	Type	Description
prompt (required)	string	The initial user prompt to start the Codex conversation.
approval-policy	string	Approval policy for shell commands generated by the model: untrusted, on-failure, on-request, never.
base-instructions	string	The set of instructions to use instead of the default ones.
config	object	Individual config settings that will override what is in $CODEX_HOME/config.toml.
cwd	string	Working directory for the session. If relative, resolved against the server process's current directory.
model	string	Optional override for the model name (e.g. o3, o4-mini).
profile	string	Configuration profile from config.toml to specify default options.
sandbox	string	Sandbox mode: read-only, workspace-write, or danger-full-access.

codex-reply - Continue a Codex session by providing the conversation id and prompt. The codex-reply tool takes the following properties:

Property	Type	Description
prompt (required)	string	The next user prompt to continue the Codex conversation.
conversationId (required)	string	The id of the conversation to continue.

Trying it Out

TIP

Codex often takes a few minutes to run. To accommodate this, adjust the MCP inspector's Request and Total timeouts to 600000ms (10 minutes) under ⛭ Configuration.

Use the MCP inspector and codex mcp-server to build a simple tic-tac-toe game with the following settings:

approval-policy: never

prompt: Implement a simple tic-tac-toe game with HTML, JavaScript, and CSS. Write the game in a single file called index.html.

sandbox: workspace-write

Click "Run Tool" and you should see a list of events emitted from the Codex MCP server as it builds the game.