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This is a very large PR with some non-backwards-compatible changes. Historically, `codex mcp` (or `codex mcp serve`) started a JSON-RPC-ish server that had two overlapping responsibilities: - Running an MCP server, providing some basic tool calls. - Running the app server used to power experiences such as the VS Code extension. This PR aims to separate these into distinct concepts: - `codex mcp-server` for the MCP server - `codex app-server` for the "application server" Note `codex mcp` still exists because it already has its own subcommands for MCP management (`list`, `add`, etc.) The MCP logic continues to live in `codex-rs/mcp-server` whereas the refactored app server logic is in the new `codex-rs/app-server` folder. Note that most of the existing integration tests in `codex-rs/mcp-server/tests/suite` were actually for the app server, so all the tests have been moved with the exception of `codex-rs/mcp-server/tests/suite/mod.rs`. Because this is already a large diff, I tried not to change more than I had to, so `codex-rs/app-server/tests/common/mcp_process.rs` still uses the name `McpProcess` for now, but I will do some mechanical renamings to things like `AppServer` in subsequent PRs. While `mcp-server` and `app-server` share some overlapping functionality (like reading streams of JSONL and dispatching based on message types) and some differences (completely different message types), I ended up doing a bit of copypasta between the two crates, as both have somewhat similar `message_processor.rs` and `outgoing_message.rs` files for now, though I expect them to diverge more in the near future. One material change is that of the initialize handshake for `codex app-server`, as we no longer use the MCP types for that handshake. Instead, we update `codex-rs/protocol/src/mcp_protocol.rs` to add an `Initialize` variant to `ClientRequest`, which takes the `ClientInfo` object we need to update the `USER_AGENT_SUFFIX` in `codex-rs/app-server/src/message_processor.rs`. One other material change is in `codex-rs/app-server/src/codex_message_processor.rs` where I eliminated a use of the `send_event_as_notification()` method I am generally trying to deprecate (because it blindly maps an `EventMsg` into a `JSONNotification`) in favor of `send_server_notification()`, which takes a `ServerNotification`, as that is intended to be a custom enum of all notification types supported by the app server. So to make this update, I had to introduce a new variant of `ServerNotification`, `SessionConfigured`, which is a non-backwards compatible change with the old `codex mcp`, and clients will have to be updated after the next release that contains this PR. Note that `codex-rs/app-server/tests/suite/list_resume.rs` also had to be update to reflect this change. I introduced `codex-rs/utils/json-to-toml/src/lib.rs` as a small utility crate to avoid some of the copying between `mcp-server` and `app-server`.
5.9 KiB
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
codex login --api-key "${{ secrets.OPENAI_KEY }}"
codex exec --full-auto "update CHANGELOG for next release"
Resuming non-interactive sessions
You can resume a previous headless run to continue the same conversation context and append to the same rollout file.
Interactive TUI equivalent:
codex resume # picker
codex resume --last # most recent
codex resume <SESSION_ID>
Compatibility:
- Latest source builds include
codex exec resume(examples below). - Current released CLI may not include this yet. If
codex exec --helpshows noresume, use the workaround in the next subsection.
# Resume the most recent recorded session and run with a new prompt (source builds)
codex exec "ship a release draft changelog" resume --last
# Alternatively, pass the prompt via stdin (source builds)
# Note: omit the trailing '-' to avoid it being parsed as a SESSION_ID
echo "ship a release draft changelog" | codex exec resume --last
# Or resume a specific session by id (UUID) (source builds)
codex exec resume 7f9f9a2e-1b3c-4c7a-9b0e-123456789abc "continue the task"
Notes:
- When using
--last, Codex picks the newest recorded session; if none exist, it behaves like starting fresh. - Resuming appends new events to the existing session file and maintains the same conversation id.
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.