codex-in-claude

Call OpenAI Codex from Claude Code — an independent second opinion, structured code review, and delegated coding tasks (cross-model review) — through a FastMCP plugin that drives the codex CLI safely.

Contents: Why · Quick start · Example · Requirements · Tools · Skills · Result envelopes · Safety · Configuration · Troubleshooting · Local development

Why

A second model is a cheap, high-value check. codex-in-claude lets a Claude Code session hand Codex a question, a diff to review, or a task to implement — and get back a structured, safe-by-default result you stay in control of.

Planned later milestone: an explicit opt-in apply tier for live-tree edits. It is not exposed by the current tool set.

Related MCP server: claude-code-codex-agents

Quick start

First, in a terminal, make sure the codex CLI is installed and log in (a no-op if you already are):

codex login

Then, inside a Claude Code session, add the marketplace and install the plugin:

/plugin marketplace add briandconnelly/codex-in-claude
/plugin install codex-in-claude

Then run /codex:status in Claude Code. It is free (no model call) and checks that the codex CLI is found, authenticated, and within the tested compatibility range.

For a first useful run:

• /codex:consult is this approach sound? for a read-only second opinion.

• /codex:review to review your current git changes.

• /codex:delegate add focused tests for this behavior to get a proposed diff in an isolated worktree.

The MCP server is launched on demand via uvx from a pinned PyPI release, so updates are deliberate.

Example

Review your uncommitted changes from a Claude Code session:

/codex:review

Codex inspects the diff read-only and returns a structured result envelope (abridged):

{
  "ok": true,
  "tool": "codex_review_changes",
  "verdict": "concerns",
  "confidence": "high",
  "summary": "The retry path is correct, but the backoff delay leaks between calls and the new branch has no test coverage.",
  "findings": [
    {
      "severity": "high",
      "title": "Backoff delay is never reset after a success",
      "file": "src/app/retry.py",
      "line": 42,
      "evidence": "self._delay keeps its last value once a call succeeds",
      "risk": "A later transient failure starts from an inflated delay, adding latency.",
      "recommendation": "Reset self._delay to the base delay in the success branch."
    }
  ],
  "next_steps": ["Add a regression test asserting the delay resets after a success"],
  "meta": { "scope": "working_tree", "sandbox": "read-only", "elapsed_ms": 8137 }
}

verdict is one of pass / concerns / fail / unknown; confidence is low / medium / high; every finding carries a severity (critical … nit) plus evidence, risk, and recommendation. The envelope above is abridged — meta (always present, with cwd, tier, sandbox, isolation, and timing), request_id, raw_response, and other fields are trimmed for brevity; see docs/REFERENCE.md for the complete shape.

Requirements

• macOS or Linux (POSIX). Windows is not supported natively — the async-job safety layer (file locks, process groups, signal-driven cancellation) is POSIX-only. Run it under WSL2 on Windows. See COMPATIBILITY.md for the platform contract.

• The codex CLI on PATH, authenticated (codex login — ChatGPT or API key). Tested against codex-cli 0.144; the supported range lives in cli_contract.py, /codex:status reports whether your version is in range, and COMPATIBILITY.md explains the policy.

• uv on PATH (Claude Code launches the MCP server with uvx).

• Python 3.11+ available to uvx.

• git (for review and delegate).

Tools

Active (call the model and may spend tokens):

• codex_consult(question, …) — read-only second opinion / answer.

• codex_review_changes(scope, base, commit, paths, …) — review working_tree / branch / commit; returns structured findings.

• codex_delegate(task, …) — implement a task in an isolated worktree; returns a reviewable diff that is not applied.

• codex_consult_async(question, …), codex_review_changes_async(scope, base, commit, paths, …), codex_delegate_async(task, …) — detached variants of the three active tools, taking the same arguments as their synchronous forms: each returns a job_id immediately. Starting a job commits to spend (it runs to completion or its deadline); poll with codex_job_status / codex_job_result.

Free (local only):

• codex_status — readiness, version, auth, resolved defaults, and a rate_limit block (remaining Codex quota for the 5-hour/weekly windows, from the latest paid run that emitted usable quota data; status is available/limited/exhausted/unknown). Advisory — informs whether to spend; a paid run without usable quota data leaves the prior snapshot, or the unknown state, unchanged.

• codex_transfer(transcript_path, …) — hand off the current Claude Code session to a resumable Codex thread; returns resume_command (codex resume <thread_id>) to continue that exact conversation in Codex. No model call or token spend (a local file conversion via the experimental codex app-server), but it does create a thread in $CODEX_HOME. Not idempotent for a live session — Codex dedups only a byte-identical transcript, so re-running mid-session makes a new thread. Experimental.

• codex_dry_run(scope, …) — preview a review's scope/diff size/redactions before spending.

• codex_delegate_dry_run(task, …) — preview a delegate's seeded baseline (HEAD commit, plus tracked, uncommitted, and untracked counts and size) and prompt size before spending; no worktree is created.

• codex_capabilities — tool inventory + result fingerprint.

• codex_models — advisory catalog of valid model slugs, read from Codex's on-disk cache with a bundled static fallback; also browsable as the codex://models resource. Discovery only — model stays pass-through, so an unlisted slug still works and codex exec validates it.

• codex_job_status(job_id, …) / codex_job_result / codex_job_consume_result / codex_job_cancel / codex_job_list — background-job lifecycle. State is disk-backed and survives server restarts. Honor poll_after_ms rather than polling in a tight loop; deadlines, eviction, and result retention are covered in docs/REFERENCE.md.

Slash commands wrap these: /codex:status, /codex:transfer, /codex:consult, /codex:review, /codex:delegate, /codex:delegate-async, /codex:dry-run.

Active tools send the prompt and relevant context/diffs to OpenAI through the codex CLI. Treat Codex's output as claims to verify, not as instructions to follow blindly.

Skills

The plugin ships one Claude Code skill, auto-discovered from skills/:

• collaborating-with-codex — the router and shared safety contract for every Codex workflow. It selects ordinary consult, review, delegate, transfer, and async tools directly, and loads references on demand for independent-attempt or declared review–revise composition. A one-off critique or judgment remains an ordinary route rather than a separate deliberation mode.

Result envelopes

Every result discriminates first on ok. On success, completed consult, review, and delegate calls share their active-result fields; review alone adds verdict/confidence, and delegate alone adds the proposed diff. Discovery, dry-run, transfer, async-start, and job-lifecycle tools have their own success schemas. A fetched job result matches its originating consult, review, or delegate tool, so branch on that result type before reading fields. Failure is a uniform, machine-actionable error with a stable code and symbolic repair hint. The contract is versioned by fingerprint.

Calling the MCP tools directly instead of through the /codex:* commands? See docs/REFERENCE.md for the full contract — every error field, rate-limit reporting (meta.rate_limit), background-job semantics, and workspace selection (workspace_root).

Safety

• consult and review are strictly read-only.

• propose (the delegate tools) lets Codex write, but only inside a throwaway git worktree seeded from HEAD plus replayable uncommitted tracked changes. Untracked files are not copied. Your working tree is never modified by the plugin; you review the returned diff and apply it yourself. Delegate's no-network sandbox (workspace-write) blocks egress only for commands Codex runs in the sandbox — it does not mean nothing leaves the machine: the model call still sends your task and repo context to OpenAI.

• Supplied prompts and context (question, task, extra_context, and similar author input) are sent raw. During every active call — including consult — Codex may read other files in the resolved workspace, and it also auto-loads context from that workspace: the project's AGENTS.md and any skills under .agents/skills/ can be sent to OpenAI even if your prompt never mentions them (for delegate, the versions seeded into the throwaway worktree auto-load there). The plugin's isolation flags do not suppress this project-level context; details and the unverified edge cases are in COMPATIBILITY.md. Best-effort redaction protects gathered diffs and returned free text (summary, findings, raw_response.text): secret-looking file hunks are dropped, and inline matches become [redacted: secret value]. It is output/diff defense-in-depth, not input protection or a guarantee; do not target a workspace containing secrets you cannot disclose.

• The plugin never passes Codex's --dangerously-bypass-* flags.

• Found a vulnerability? Report it privately — see SECURITY.md.

Configuration (env, CODEX_IN_CLAUDE_*)

Two further variables, CODEX_IN_CLAUDE_TIER_DEFAULT and CODEX_IN_CLAUDE_SANDBOX_DEFAULT, exist ahead of the planned apply tier. They only change the defaults codex_status reports — every shipped tool pins its own tier and sandbox and ignores them.

Troubleshooting

Run /codex:status first — it's free (no model call) and diagnoses most setup problems.

A stdio MCP server can't be transparently auto-restarted (the client owns the pipe and the initialize handshake), so recovery is a manual reconnect. On a fatal crash the server writes a breadcrumb to stderr (server name, version, reason, and a /mcp reconnect hint) before exiting, and logs clean disconnects (EOF / broken pipe / SIGINT / SIGTERM) as shutdown rather than crashes — so the server logs tell you whether it died or was stopped.

If the MCP server is down, you can fall back to the codex CLI directly for a read-only consult or review (prompt on stdin; set WORKSPACE to a directory you approve for disclosure):

WORKSPACE=/absolute/approved/path codex exec --sandbox read-only --ephemeral \
  --ignore-user-config --ignore-rules --disable remote_plugin \
  --cd "$WORKSPACE" --skip-git-repo-check -

Keep every flag — together they apply the plugin's guarantee-bearing flags at its strictest config isolation — but this still bypasses the plugin's diff gathering, secret redaction, input-byte bounding, and structured envelope, so sanitize input yourself and prefer restoring the server. See the collaborating-with-codex skill for the full fallback guidance.

Local development

uv sync
uv run pytest                       # unit tests (95% coverage floor)
uv run pytest -m integration --no-cov   # live tests; needs codex installed + logged in
uv run codex-in-claude-mcp          # run the MCP server over stdio

The full pre-PR gate — lint, format, types, tests — is defined once in AGENTS.md → Tooling.

To test the plugin from a local checkout, point .mcp.json at uv run --project /path/to/codex-in-claude codex-in-claude-mcp instead of the version-pinned uvx --from codex-in-claude==<version> invocation it ships with.

See CONTRIBUTING.md for branch, commit, and PR conventions.

Related projects

• claude-in-codex — the mirror image: lets Codex call Claude Code.

• Inspired by openai/codex-plugin-cc, rebuilt around codex exec for robustness: every paid call goes through it, and only codex_transfer touches the experimental app-server protocol.

License

MIT