Ask Codex MCP

MCP server that connects any AI client to OpenAI Codex CLI

An MCP server for AI-to-AI collaboration via the Codex CLI. Works with Claude Code, Claude Desktop, Cursor, Warp, Copilot, and 40+ other MCP clients. Access GPT-5.5 for code generation, analysis, and review with automatic fallback to GPT-5.4-mini on quota limits.

Part of the Ask LLM monorepo.

Quick Start

Claude Code

claude mcp add codex -- npx -y @ask-llm/codex-mcp

Claude Desktop

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "codex": {
      "command": "npx",
      "args": ["-y", "@ask-llm/codex-mcp"]
    }
  }
}

Any MCP Client

{
  "command": "npx",
  "args": ["-y", "@ask-llm/codex-mcp"]
}

Prerequisites

• Node.js v20.0.0 or higher
• Codex CLI installed and authenticated

Tools

| Tool | Purpose | |------|---------| | ask-codex | Send prompts to Codex CLI. Defaults to GPT-5.6 Sol at medium effort with automatic Terra fallback; optional reasoningEffort override | | ping | Connection test — verify MCP setup without using tokens |

Models

| Model | Use Case | |-------|----------| | gpt-5.6-sol | Default — flagship capability | | gpt-5.6-terra | Automatic balanced fallback on quota errors |

Environment variables

| Variable | Default | Purpose | |----------|---------|---------| | ASK_CODEX_MODEL | gpt-5.6-sol | Override the default model | | ASK_CODEX_PREFERRED_MODEL | gpt-5.6-sol | Legacy review-tier escape hatch; only attempted separately when it differs from the default | | ASK_CODEX_FALLBACK_MODEL | gpt-5.6-terra | Override the quota-fallback model | | ASK_CODEX_REASONING_EFFORT | medium | Default reasoning effort (low, medium, high, xhigh, or max); per-call reasoningEffort wins | | ASK_CODEX_LOAD_USER_CONFIG | (unset) | Set to 1 to opt back into loading ~/.codex/config.toml (hooks, MCP servers, preferences) and execpolicy .rules files. By default the wrapper passes --ignore-user-config --ignore-rules so behavior stays deterministic across host machines. Auth credentials in CODEX_HOME always load regardless. See ADR-071. | | ASK_CODEX_TIMEOUT_MS | 800000 | Per-call timeout for the spawned codex process (13.3 min — reasoning models routinely take 5–10 min on substantive prompts; raised in ADR-074) | | GMCPT_TIMEOUT_MS | (unset) | Cross-provider timeout override; lower precedence than ASK_CODEX_TIMEOUT_MS | | GMCPT_LOG_LEVEL | warn | debug, info, warn, or error |

Documentation

Full docs at lykhoyda.github.io/ask-llm

License

MIT