Advanced
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" }
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, 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. |
include-plan-tool |
boolean | Whether to include the plan tool in the conversation. |
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.