Codex In Claude

CI License: MIT Python PyPI

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.

Tier	Codex sandbox	Where edits go	Use for
consult	read-only	nothing — text/findings only	questions, second opinions
review	read-only	nothing — structured findings	reviewing your git changes
propose (the delegate tools)	workspace-write (temp git worktree)	isolated worktree → returns a reviewable diff, never auto-applied	delegating a coding task

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

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",
  "review_status": "completed",
  "coverage": { "status": "complete", "untracked_files_detected": 0, "untracked_files_omitted": 0, "omission_reasons": [] },
  "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. verdict is the safe overall conclusion: review_status tells you whether the model actually ran (a tree with nothing reviewable returns not_run/unknown, never a false pass), and coverage discloses anything the model was not shown — omitted untracked files (governed by the untracked policy), a truncated diff, or a redacted file — downgrading a pass over partial coverage to unknown. 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 shorter/rolling and longer windows, read live from the Codex app-server with no model spend; status is available/limited/exhausted/unknown/ unavailable). Advisory — informs whether to spend; unknown/unavailable mean no usable reading, not a problem.
• 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/review_status/coverage, 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_*)

Var	Default	Meaning
CODEX_IN_CLAUDE_MODEL	unset	Codex model override
CODEX_IN_CLAUDE_REASONING_EFFORT	unset	Codex reasoning-effort override, sent as a model_reasoning_effort config override on every paid call; an open per-model string the Codex backend validates — codex_models lists each model's advertised set (semantics and probes in COMPATIBILITY.md). The per-call reasoning_effort parameter overrides it; a backend-rejected value fails as invalid_reasoning_effort
CODEX_IN_CLAUDE_TIMEOUT_SECONDS	180	per-call timeout (clamped 10–600)
CODEX_IN_CLAUDE_ISOLATION	inherit	inherit | ignore-config | ignore-rules
CODEX_IN_CLAUDE_EXTRA_ARGS	unset	extra global codex options added to every paid exec call (consult/review/delegate), so you can select a model_provider/--profile even under ignore-config isolation (which drops config.toml, leaving -c the only lever). Allowlist only: -c/--config KEY=VALUE, -p/--profile NAME, --enable/--disable FEATURE. Anything else is refused with extra_args_rejected before any spend — including -c keys under sandbox/approval_policy/shell_environment_policy (guarantee-weakening) and the reserved model/model_reasoning_effort keys, plus their case/quote lookalikes (use CODEX_IN_CLAUDE_MODEL/CODEX_IN_CLAUDE_REASONING_EFFORT or the per-call model/reasoning_effort parameters instead; deny rules and rationale in COMPATIBILITY.md). -c values may hold secrets, so they are never echoed in codex_status or errors. A --profile layers an on-disk TOML this server cannot inspect — an operator-trust boundary (see COMPATIBILITY.md)
CODEX_IN_CLAUDE_MAX_INPUT_BYTES	200000	byte cap on author input: gathered diffs are truncated to it, author text above it is rejected with input_too_large (consult counts question+extra_context together; review/delegate cap each input separately)
CODEX_IN_CLAUDE_MAX_DELEGATE_DIFF_BYTES	200000	cap on the inline diff a delegate run returns; larger diffs are truncated with meta.truncated/meta.truncation_hint (min 1000)
CODEX_IN_CLAUDE_MAX_OUTPUT_BYTES	10485760	byte cap for captured stdout (head+tail window; run not killed); stderr is bounded to a separate ~1 MiB reserve
CODEX_IN_CLAUDE_GIT_TIMEOUT_SECONDS	60	git command timeout
CODEX_IN_CLAUDE_STATE_DIR	$XDG_CACHE_HOME/codex-in-claude/jobs or ~/.cache/codex-in-claude/jobs	disk-backed background-job records
CODEX_IN_CLAUDE_JOB_TTL	86400	seconds a finished job record is kept (min 60)
CODEX_IN_CLAUDE_JOB_MAX_SECONDS	1800	background-job wall-clock cap (clamped 60–7200)
CODEX_IN_CLAUDE_JOB_MAX_COUNT	50	retained jobs per workspace (clamped 1–1000)
CODEX_IN_CLAUDE_SUPPORTED_VERSIONS	built-in tested set	comma-separated codex major.minor versions to treat as supported
CODEX_IN_CLAUDE_LOG_LEVEL	WARNING	server diagnostic log level (DEBUG|INFO|WARNING|ERROR|CRITICAL); logs go to stderr (never stdout)
CODEX_IN_CLAUDE_LOG_FILE	unset	also mirror diagnostic logs to this file path
CODEX_IN_CLAUDE_ALLOW_UNSUPPORTED_PLATFORM	unset	set to 1 to downgrade the non-POSIX startup refusal to a stderr warning for knowingly consult-only, unsupported use; the async-job safety layer cannot hold, so do not run delegate/review against untrusted work (see Requirements / COMPATIBILITY.md)

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.

Symptom	Cause	Fix
codex not found	CLI not installed or not on PATH	Install the codex CLI and ensure it's on PATH
Not authenticated	No Codex login	codex login (ChatGPT or API key)
Unsupported-version warning	Your codex version is outside the tested range	Update codex, or set CODEX_IN_CLAUDE_SUPPORTED_VERSIONS once you've verified it works
meta.workspace_warning in results	Server fell back to its own launch directory	Run from the target repo, or pass workspace_root (see docs/REFERENCE.md)
codex_delegate fails needing a commit	The temp worktree is seeded from HEAD	Make at least one commit first
codex_rate_limited error	Account hit a usage/rate limit	Back off for retry_after_ms, then retry
Connection closed / No such tool available: mcp__codex-in-claude__*	The stdio MCP server is down	Reconnect with the /mcp command (or restart the client), then confirm with codex_status; see the fallback note below

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