Codex Octopus

Codex Octopus

One brain, many arms.

An MCP server that wraps the OpenAI Codex SDK, letting you run multiple specialized Codex agents — each with its own model, sandbox, effort, and personality — from any MCP client.

Why

Codex is powerful. But one instance does everything the same way. Sometimes you want a strict code reviewer in read-only sandbox. A test writer with workspace-write access. A cheap quick helper on minimal effort. A deep thinker on xhigh.

Codex Octopus lets you spin up as many of these as you need. Same binary, different configurations. Each one shows up as a separate tool in your MCP client.

Prerequisites

• Node.js >= 18
• Codex CLI — the Codex SDK spawns the Codex CLI under the hood, so you need it installed (@openai/codex)
• OpenAI API key (CODEX_API_KEY env var) or inherited from parent process

Install

npm install codex-octopus

Or use npx directly in your .mcp.json (see Quick Start below).

Quick Start

Add to your .mcp.json:

{
  "mcpServers": {
    "codex": {
      "command": "npx",
      "args": ["codex-octopus@latest"],
      "env": {
        "CODEX_SANDBOX_MODE": "workspace-write",
        "CODEX_APPROVAL_POLICY": "never"
      }
    }
  }
}

This gives you two tools: codex and codex_reply. That's it — you have Codex as a tool.

Multiple Agents

The real power is running several instances with different configurations:

{
  "mcpServers": {
    "code-reviewer": {
      "command": "npx",
      "args": ["codex-octopus@latest"],
      "env": {
        "CODEX_TOOL_NAME": "code_reviewer",
        "CODEX_SERVER_NAME": "code-reviewer",
        "CODEX_DESCRIPTION": "Strict code reviewer. Read-only sandbox.",
        "CODEX_MODEL": "o3",
        "CODEX_SANDBOX_MODE": "read-only",
        "CODEX_APPEND_INSTRUCTIONS": "You are a strict code reviewer. Report real bugs, not style preferences.",
        "CODEX_EFFORT": "high"
      }
    },
    "test-writer": {
      "command": "npx",
      "args": ["codex-octopus@latest"],
      "env": {
        "CODEX_TOOL_NAME": "test_writer",
        "CODEX_SERVER_NAME": "test-writer",
        "CODEX_DESCRIPTION": "Writes thorough tests with edge case coverage.",
        "CODEX_MODEL": "gpt-5-codex",
        "CODEX_SANDBOX_MODE": "workspace-write",
        "CODEX_APPEND_INSTRUCTIONS": "Write tests first. Cover edge cases. TDD."
      }
    },
    "quick-qa": {
      "command": "npx",
      "args": ["codex-octopus@latest"],
      "env": {
        "CODEX_TOOL_NAME": "quick_qa",
        "CODEX_SERVER_NAME": "quick-qa",
        "CODEX_DESCRIPTION": "Fast answers to quick coding questions.",
        "CODEX_EFFORT": "minimal"
      }
    }
  }
}

Your MCP client now sees three distinct tools — code_reviewer, test_writer, quick_qa — each purpose-built.

Agent Factory

Don't want to write configs by hand? Add a factory instance:

{
  "mcpServers": {
    "agent-factory": {
      "command": "npx",
      "args": ["codex-octopus@latest"],
      "env": {
        "CODEX_FACTORY_ONLY": "true",
        "CODEX_SERVER_NAME": "agent-factory"
      }
    }
  }
}

This exposes a single create_codex_mcp tool — an interactive wizard. Tell it what you want ("a strict code reviewer with read-only sandbox") and it generates the .mcp.json entry for you.

Tools

Each non-factory instance exposes:

Tool	Purpose
<name>	Send a task to the agent, get a response + thread_id
<name>_reply	Continue a previous conversation by thread_id

Per-invocation parameters (override server defaults):

Parameter	Description
prompt	The task or question (required)
cwd	Working directory override
model	Model override
additionalDirs	Extra directories the agent can access
effort	Reasoning effort (minimal to xhigh)
sandboxMode	Sandbox override (can only tighten, never loosen)
approvalPolicy	Approval override (can only tighten, never loosen)
networkAccess	Enable network access from sandbox
webSearchMode	Web search: disabled, cached, live
instructions	Additional instructions (prepended to prompt)

Configuration

All configuration is via environment variables in .mcp.json. Every env var is optional.

Identity

Env Var	Description	Default
CODEX_TOOL_NAME	Tool name prefix (<name> and <name>_reply)	codex
CODEX_DESCRIPTION	Tool description shown to the host AI	generic
CODEX_SERVER_NAME	MCP server name in protocol handshake	codex-octopus
CODEX_FACTORY_ONLY	Only expose the factory wizard tool	false

Agent

Env Var	Description	Default
CODEX_MODEL	Model (gpt-5-codex, o3, codex-1, etc.)	SDK default
CODEX_CWD	Working directory	process.cwd()
CODEX_SANDBOX_MODE	read-only, workspace-write, danger-full-access	read-only
CODEX_APPROVAL_POLICY	never, on-failure, on-request, untrusted	on-failure
CODEX_EFFORT	minimal, low, medium, high, xhigh	SDK default
CODEX_ADDITIONAL_DIRS	Extra directories (comma-separated)	none
CODEX_NETWORK_ACCESS	Allow network from sandbox	false
CODEX_WEB_SEARCH	disabled, cached, live	disabled

Instructions

Env Var	Description
CODEX_INSTRUCTIONS	Replaces the default instructions
CODEX_APPEND_INSTRUCTIONS	Appended to the default (usually what you want)

Advanced

Env Var	Description
CODEX_PERSIST_SESSION	true/false — enable session resume (default: true)

Authentication

Env Var	Description	Default
CODEX_API_KEY	OpenAI API key for this agent	inherited from parent

Security

• Sandbox defaults to read-only — the agent can't write files unless you explicitly set workspace-write or danger-full-access.
• cwd overrides preserve agent knowledge — when the host overrides cwd, the agent's configured base directory is automatically added to additionalDirectories.
• Security overrides narrow, never widen — per-invocation sandboxMode and approvalPolicy can only tighten (e.g., workspace-write → read-only), never loosen.
• _reply tool respects persistence — not registered when CODEX_PERSIST_SESSION=false.
• API keys are redacted — the factory wizard never exposes CODEX_API_KEY in generated configs.

Architecture

┌─────────────────────────────────┐
│  MCP Client                     │
│  (Claude Desktop, Cursor, etc.) │
│                                 │
│  Sees: code_reviewer,           │
│        test_writer, quick_qa    │
└──────────┬──────────────────────┘
           │ JSON-RPC / stdio
┌──────────▼──────────────────────┐
│  Codex Octopus (per instance)   │
│                                 │
│  Env: CODEX_MODEL=o3            │
│       CODEX_SANDBOX_MODE=...    │
│       CODEX_APPEND_INSTRUCTIONS │
│                                 │
│  Calls: Codex SDK thread.run()  │
└──────────┬──────────────────────┘
           │ in-process
┌──────────▼──────────────────────┐
│  Codex SDK → Codex CLI          │
│  Runs autonomously: reads files,│
│  writes code, runs commands     │
│  Returns result + thread_id     │
└─────────────────────────────────┘

Known Limitations

• minimal effort + web_search: OpenAI does not allow web_search tools with minimal reasoning effort. Use low or higher if web search is needed.

Development

pnpm install
pnpm build       # compile TypeScript
pnpm test        # run tests (vitest)
pnpm test:coverage  # coverage report

License

ISC - Xiaolai Li