Subcodex

MCP server for Claude Code to use OpenAI Codex as a subagent, with stall detection and auto-recovery.

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Why subcodex?

Claude Code and Codex have complementary strengths:

Role	Claude Code	Codex
Analogy	Product Manager who understands requirements	Technical expert in deep focus
Strengths	Planning, communication, context understanding	Coding, debugging, implementation
Best at	Breaking down tasks, writing specs, verification	Writing code, fixing bugs, refactoring

subcodex bridges these two, letting Claude Code orchestrate Codex as a subagent:

• Claude Code handles the "what" and "why" (requirements, planning, verification)
• Codex handles the "how" (implementation, debugging)

This combination delivers better results than either tool alone.

Features

• Run Codex sessions with streaming progress
• Automatic stall detection (configurable timeout)
• Auto-recovery attempts when stalled
• Progress logging to ~/.claude/codex-logs/
• Thread continuation support via codex-reply

Usage Modes

Configure in your CLAUDE.md to control when subcodex is used:

Mode 1: Full Subagent

All code modifications go through subcodex. Claude only does analysis, planning, and verification.

## Subagent Mode: full-subagent

All code changes must go through `mcp__subcodex__run`:
- Claude: analyze, plan, write Codex Contract, verify results
- Subcodex: all file edits, code generation, refactoring

Mode 2: Directory-Based

Different directories are handled by different executors.

## Subagent Mode: directory-based

| Scope | Executor |
|-------|----------|
| `apps/web/**/*` | Claude direct |
| `apps/api/**/*`, `packages/**/*` | subcodex |
| docs, config | Claude direct |

Mode 3: Fallback

Claude handles everything, but falls back to subcodex on failure.

## Subagent Mode: fallback

- Claude attempts all code changes directly
- After 2 failed attempts → automatically use subcodex
- Windows file lock errors → immediately use subcodex

Installation

From npm

npx subcodex-mcp

From source

git clone https://github.com/G0d2i11a/subcodex.git
cd subcodex
pnpm install
pnpm build

Configuration

Add to your Claude Code MCP config (~/.claude.json):

{
  "mcpServers": {
    "subcodex": {
      "command": "npx",
      "args": ["-y", "subcodex-mcp"],
      "env": {},
      "type": "stdio"
    }
  }
}

Or for local development:

{
  "mcpServers": {
    "subcodex": {
      "command": "node",
      "args": ["/path/to/subcodex/dist/index.js"],
      "env": {},
      "type": "stdio"
    }
  }
}

Tools

run

Start a new Codex session.

Parameter	Type	Required	Description
prompt	string	Yes	The prompt to send to Codex
cwd	string	No	Working directory for the session
model	string	No	Model override (e.g., 'gpt-5.2')
sandboxMode	string	No	read-only, workspace-write, or danger-full-access
approvalPolicy	string	No	never, on-request, on-failure, or untrusted
level	string	No	Execution level: L1, L2, L3, L4 (for log naming)
stallTimeoutMinutes	number	No	Minutes of inactivity before detecting stall (default: 5)
maxRecoveryAttempts	number	No	Max auto-recovery attempts when stalled (default: 2)

reply

Continue an existing Codex conversation.

Parameter	Type	Required	Description
threadId	string	Yes	The thread ID from a previous session
prompt	string	Yes	The next prompt to continue the conversation
level	string	No	Execution level for log naming
stallTimeoutMinutes	number	No	Minutes of inactivity before detecting stall (default: 5)
maxRecoveryAttempts	number	No	Max auto-recovery attempts when stalled (default: 2)

Stall Detection

The server monitors Codex sessions for activity. If no events are received within the timeout period:

1. Marks the session as stalled
2. Attempts auto-recovery by sending a recovery prompt
3. Retries up to maxRecoveryAttempts times
4. Returns TIMEOUT status with needsUserInput: true if all recovery attempts fail

Handling needsUserInput

When the response contains needsUserInput: true, Claude should use AskUserQuestion to ask the user how to proceed. Add this rule to your CLAUDE.md:

## Subcodex Stall Handling

When `mcp__subcodex__run` returns `needsUserInput: true`:
- Use AskUserQuestion to ask the user how to proceed
- Options: retry, skip current task, manual intervention

Response Format

{
  "threadId": "abc123...",
  "level": "L2",
  "content": "Final response from Codex",
  "progressLog": "~/.claude/codex-logs/progress-L2-xxx-PASS.log",
  "stats": {
    "totalItems": 10,
    "commands": 3,
    "fileChanges": 2,
    "mcpCalls": 0,
    "usage": {
      "input_tokens": 1000,
      "output_tokens": 500
    }
  },
  "filesModified": ["create: src/foo.ts", "modify: src/bar.ts"],
  "recovery": {
    "attempted": false
  },
  "needsUserInput": false
}

When stalled and recovery fails:

{
  "threadId": "abc123...",
  "level": "L2",
  "content": "",
  "progressLog": "~/.claude/codex-logs/progress-L2-xxx-TIMEOUT.log",
  "recovery": {
    "attempted": true,
    "attempts": 2,
    "recovered": false,
    "lastError": "Still stalled after recovery attempt"
  },
  "needsUserInput": true
}

Result Levels

Log files are renamed with result level suffix:

• PASS - Success (log file deleted)
• FAIL - Command or file change failed
• ERROR - Exception occurred
• TIMEOUT - Stalled and recovery failed

Requirements

• Node.js 18+
• OpenAI Codex SDK credentials configured

License

MIT