Codex CLI Subagent

This skill lets you spawn a nested Codex process (a “subagent”) using codex exec so it can work with the same project and AGENTS.md instructions.

filename="$(openssl rand -hex 4)"
codex exec "count the total number of lines of code in this project" 2>>/tmp/${filename}.log

In non-interactive mode, codex exec runs without a TUI and follows the configured approval/sandbox policy (flags and/or ~/.codex/config.toml). By default it runs in read-only mode, so it cannot edit files or run commands that require network access.

When you use this skill, follow these logging rules:

• Before running codex exec, generate a unique log file name with openssl rand -hex 4.
• By default, append 2>>/tmp/${filename}.log to your codex exec command so only the subagent’s final message is visible to the caller, while stderr is captured for debugging.
• If a run fails, behaves unexpectedly, or the user explicitly asks to see what the inner agent is doing, read the log file (for example: cat /tmp/${filename}.log).

Since the codex exec may run couple hours, set a generous timeout so long-running subagent work can complete:

• Use a timeout of at least 60 minutes for the Run (or Bash) tool unless the user explicitly requests other limit.

Use this skill when you want a focused helper agent (for refactors, audits, scripted operations, or scans) while keeping your main session and context intact.

Use codex exec --full-auto to allow file edits. Use codex exec --sandbox danger-full-access to allow edits and networked commands, but only when the user clearly permits this level of access.

Practical gotchas

• Prefer stdin for long prompts to avoid shell quoting/globbing issues: codex exec - < /tmp/prompt.md.
• If you need built-in web search, pass --search (otherwise assume “no web tool” and use curl/repo sources).
• Don’t run nested subagents (avoid calling codex exec from inside a codex exec session).
• Consider --output-last-message /tmp/${filename}.out to capture the final answer without scraping logs.

Key Flags

• --full-auto: Unattended operation with workspace-write sandbox
• --dangerously-bypass-approvals-and-sandbox or --yolo: Complete hands-off mode (use carefully)
• --cd <path>: Set working directory
• --model <model> or -m: Specify model (e.g., -m gpt-5.1-codex-max)
• --sandbox: Sandbox types:
  • read-only: No file edits, no networked commands
  • workspace-write: Can edit files in the workspace
  • danger-full-access: No sandboxing; full access (use with care)
• --search: Enable built-in web search tool
• --config: Pass config variables:
  • model_reasoning_effort: Model reasoning effort: low, medium, high;

Examples

# As a subagent, perform automated refactoring
filename="$(openssl rand -hex 4)"
codex exec --full-auto "Update all README links to HTTPS" 2>>/tmp/${filename}.log

# Run in a specific project directory
filename="$(openssl rand -hex 4)"
codex exec --cd /path/to/project "Fix failing tests" 2>>/tmp/${filename}.log

# Use AGENTS.md context for a focused refactor
filename="$(openssl rand -hex 4)"
codex exec --cd /path/to/project "Using this repo's AGENTS.md instructions, refactor the test helpers for clarity and consistency" 2>>/tmp/${filename}.log

filename="$(openssl rand -hex 4)"
codex exec --model gpt-5.1-codex-max --sandbox workspace-write --config model_reasoning_effort=medium - < /tmp/some-big-prompt.md 2>>/tmp/${filename}.log

# For audits / deep analysis
filename="$(openssl rand -hex 4)"
codex exec --model gpt-5.2 --sandbox read-only --config model_reasoning_effort=high "Audit this repo for security issues" 2>>/tmp/${filename}.log

Input Methods

# Pipe prompt from file
filename="$(openssl rand -hex 4)"
codex exec - < prompt.txt 2>>/tmp/${filename}.log

# Standard input
filename="$(openssl rand -hex 4)"
echo "Review this code" | codex exec - 2>>/tmp/${filename}.log

When this skill is invoked, you should decide:

• Whether a subagent is appropriate (e.g., long-running refactor, scan, or analysis).
• Which flags, sandbox level, and model to use based on user intent and risk.
• For code changes: default to --model gpt-5.1-codex-max --config model_reasoning_effort=medium unless the user explicitly requests otherwise.
• For audits: default to --model gpt-5.2 --config model_reasoning_effort=high unless the user explicitly requests otherwise.
• Whether to keep logs suppressed (default: 2>>/tmp/${filename}.log or read/tail /tmp/${filename}.log)