ultracodex

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Claude orchestrates. Codex cross-checks. Blend Codex headless (codex exec) nodes into Claude Code's own Workflow (ultracode) orchestration — so a genuinely different model family verifies, judges, and second-guesses at the points where same-model agreement is least trustworthy.

ultracodex is an open-source Claude Code plugin — a single skill, codex-workflow — that teaches Claude how to mix Codex headless nodes into a Workflow: Claude Code's agent() / pipeline() / parallel() orchestration tool, a.k.a. ultracode. The orchestration logic stays in Claude's JavaScript; only who does the work changes at chosen nodes. This is "Pattern A" — and it is additive, not a model-switcher. Both families run in one Workflow.

Workflow (Claude JS orchestration)
 ├─ find / generate / synthesize .. Claude agent()  ← broad, fast, cache-warm
 └─ verify / judge / 2nd-opinion ... codex node     ← GPT, independent failure modes

Requires ultracode mode. Because the skill authors and runs Workflows, the Workflow orchestration tool must be available — which in Claude Code means ultracode mode (enable it with /effort → ultracode; it turns on dynamic workflow orchestration). Without it the plugin still loads and the skill is found, but there is no Workflow tool to drive. See Prerequisites.

Why it exists — the philosophy

More verifiers from the same model tend to share that model's blind spots: they re-confirm the same correlated false positives. A different model family fails on different inputs, so it can refute what same-model reviewers would rubber-stamp. That is the whole idea:

• Diversity, not replacement. The win comes from disagreement between independent models, so the goal is to keep both families in one run — never to swap Claude out. "Add a second opinion" is right; "use GPT instead" misses the point.
• Independent failure modes beat more of the same. Routing a verify/judge node to Codex reduces correlated error — the kind N more Claude verifiers cannot catch because they fail in the same places.
• The orchestration stays in Claude. Claude holds the context, schemas, fan-out, and synthesis. A codex node is just a normal agent() whose subagent relays a codex exec run. No Workflow primitive changes — a low-surface-area way to get cross-model value.
• A second model is not a source of truth. It is another failure-mode distribution, best combined with tests, evidence, strict schemas, and a final Claude synthesis. "Independent" is also relative: a shared prompt, shared evidence, or a loose schema can still correlate errors — so use Codex deliberately, where there is a verifiable artifact to check.

What you gain

• Catch false positives that survive same-model review — a different model family can refute some correlated Claude errors before you act on a finding or claim (a reduction in correlated error, not a guarantee).
• Higher-trust verdicts on risky conclusions — cross-check a headline result with a model that didn't produce it, before you report or ship.
• Genuinely diverse judge panels — score candidates with a jury where no model only judges its own work, cutting self-preference bias in LLM-as-judge setups.
• Real solution diversity in generation — a Codex attempt in an N-way panel is a different family's answer, not a reworded Claude one.
• Large-context, multi-file verification with no new machinery — point Codex at a tree (cwd / -C; read-only blocks writes, not reads) so it reads big diffs and files itself instead of you pasting them into a prompt.
• Copy-paste ready — four complete Workflow templates (cross-model review, mixed judge panel, single-conclusion cross-check, loop-until-dry) plus the canonical codexNode helper. You start from working scripts, not a blank file.
• Minimal surface change — keep every Workflow primitive exactly as-is; only the chosen nodes change hands.

The highest-ROI use: adversarial verification

Claude finds broadly; Codex tries to refute each finding (defaulting to "refuted" when uncertain). Survivors are the findings a different model family could not knock down — a pipeline, no barrier:

const results = await pipeline(
  DIMENSIONS,
  d => agent(d.findPrompt, { phase: 'Find', schema: FINDINGS }),         // Claude finds
  review => parallel((review?.findings ?? []).map(f => () =>
    codexNode(`Adversarially verify, defaulting to refuted=true if uncertain:\n${f.title}\n${f.detail}`,
      { schema: VERDICT, phase: 'Verify', label: `codex:${f.id}` })       // Codex refutes
      .then(v => ({ ...f, verdict: v })))),
)
const confirmed = results.flat().filter(Boolean)
  .filter(f => f.verdict && !f.verdict._codex_error && f.verdict.refuted === false)

Mixed judge panels and single-conclusion second opinions are the next tiers — full scripts in workflow-templates.md.

When to use it — and when not to

Cross-model is signal, not free signal. Reach for a codex node when a second, independent model materially de-risks the result — verifying findings, judging candidates, an independent attempt in a panel, sanity-checking a risky conclusion.

Skip the blend when:

• it's bulk throughput work (Claude subagents are cheaper, faster, cache-warm);
• it's a correlated check — Codex would only re-derive from the same evidence, an echo rather than a second opinion;
• it's a blind check — the node can't give Codex what it needs to verify independently;
• there's no verifiable/judgeable artifact (open-ended ideation) — diversity adds noise, not signal.

Prerequisites

• Ultracode mode — the Workflow tool. The skill authors and runs Workflows, so the Workflow tool (agent()/pipeline()/parallel()) must be available. In Claude Code that means ultracode mode: enable it with /effort → ultracode (xhigh + dynamic workflow orchestration). The skill only provides the know-how for authoring Workflows; it does not add the tool itself, so without ultracode mode it has nothing to drive.
• Codex CLI, installed and authenticated. Verify, then log in (interactive — it cannot be done headlessly):
  copy

  command -v codex && codex --version
  codex login
  

• A POSIX shell (bash/zsh) for the relay nodes.

The skill hard-codes no Codex version or default model — environments differ. It ships a cheap preflight (CLI present, auth live, structured-output path) to run once before trusting any node.

Installation

ultracodex is its own single-plugin marketplace. Add it, install the plugin, reload:

/plugin marketplace add KingGyuSuh/ultracodex
/plugin install ultracodex@ultracodex
/reload-plugins

Non-interactive (CLI) equivalent:

claude plugin marketplace add KingGyuSuh/ultracodex
claude plugin install ultracodex@ultracodex
# then restart Claude Code, or run /reload-plugins in an existing session

The @ultracodex suffix on install is the marketplace name (top-level name in .claude-plugin/marketplace.json), independent of the repo name — they happen to match here.

Try it without installing

claude --plugin-dir ./plugins/ultracodex

Usage

The skill triggers automatically when you ask Claude to run a task as a custom Workflow with a second model in the loop. Phrasings that activate it include:

• "Run this as a custom workflow that mixes in codex."
• "Have codex adversarially verify the findings."
• "Use codex as a juror / second opinion in the workflow."
• "Cross-model verify this while you orchestrate."

Claude then authors a Workflow whose verify/judge nodes shell out to codex exec while find/generate/synthesize stay on Claude — starting from a template.

How it works — the codex node

A Workflow script's JS body has no filesystem access, so a codex node embeds its JSON Schema as a string and lets the Bash-capable wrapper subagent write it to a temp file. One schema object is the single source of truth: it feeds Codex's --output-schema and, when revalidate is true, the agent() re-validation. With the default revalidate: true the node returns a parsed object; with revalidate: false it relays raw JSON text for the caller to JSON.parse. The contract:

codexNode(taskText, { schema, sandbox='read-only', model, cwd, effort, revalidate=true, phase, label })
  → Promise<parsedObject>   // revalidate:true (default)
  → Promise<string>         // revalidate:false — you JSON.parse it
  → { _codex_error: true }  // on failure

Three rules are load-bearing:

1. Relay, not solver. The wrapping Claude subagent is smart and will be tempted to just answer the question — silently collapsing the cross-model node back into a Claude node. The prompt forbids this; keep it at full strength.
2. Extract from the -o file, not stdout. stdout carries session chrome; -o is the one clean-JSON path.
3. Pass the prompt via stdin (- < "$TASK") so quotes, $, and backticks can't break or expand.

The full copy-paste helper lives canonically in workflow-templates.md; the mechanics, flags, sandbox tiers, troubleshooting, and escalation patterns are in codex-headless.md.

Routing: Codex node vs Claude node

Cost, concurrency & escalation

• Two billing surfaces. Every codex node pays the Anthropic wrapper turn plus the Codex/OpenAI run. The wrapper only relays, but it still has a subagent's fixed overhead — don't fan out hundreds casually; batch small items instead.
• Keep codex nodes short. Each holds a Workflow concurrency slot (min(16, cores−2)) for Codex's entire runtime while the wrapper idles on a blocking Bash call. Read-only verify/judge/small-gen only.
• Escalate long work. Minutes-to-hours, parallel, or resumable Codex jobs are not Pattern A — use a background worker pool or a single-shot handoff (described in the skill), never a long node inside a Workflow.

What's in the box

A single skill, codex-workflow:

• SKILL.md — the mental model, the codexNode contract, the load-bearing rules, routing, cost/concurrency, and the preflight.
• references/codex-headless.md — codex exec flags, sandbox tiers, output extraction, gotchas, troubleshooting, the _codex_error discipline, and escalation patterns.
• references/workflow-templates.md — the canonical codexNode helper and four complete Workflow scripts, plus batch-node and large-payload variants.

ultracodex/                              # repo root = marketplace root
├── .claude-plugin/
│   └── marketplace.json                 # single-plugin marketplace catalog
├── plugins/
│   └── ultracodex/                      # the plugin
│       ├── .claude-plugin/
│       │   └── plugin.json              # plugin manifest
│       ├── README.md
│       └── skills/
│           └── codex-workflow/
│               ├── SKILL.md
│               └── references/
│                   ├── codex-headless.md
│                   └── workflow-templates.md
├── docs/                                # README translations (ko / ja / zh-CN)
├── LICENSE                              # Apache-2.0
├── NOTICE
└── README.md

Scope is deliberately skill-only: no commands, agents, hooks, or MCP servers.

Development

claude plugin validate ./plugins/ultracodex   # plugin manifest + skill frontmatter
claude plugin validate .                       # marketplace manifest
claude plugin tag ./plugins/ultracodex         # cut a release tag (manifests must agree)

Acknowledgements

The codex-workflow skill is the open-source generalization of a private in-repo skill of the same name. This release removes environment-specific facts (it preflights instead) and private path references, and was itself developed and cross-checked using the plugin's own blended Claude+Codex workflows — including this README, drafted and proofread cross-model.

License

Apache-2.0 © 2026 KingGyuSuh