Codex CLI Skill

⚠️ Environment Notice

Environment	Git Repo	Command Format
Interactive terminal	Any	`codex "prompt"`
Claude Code / CI	✅ Yes	`codex exec -s read-only "prompt"`
Claude Code / CI	❌ No	`codex exec --skip-git-repo-check -s read-only "prompt"`

Non-TTY environments (Claude Code, CI pipelines, scripts) require codex exec.

Git Repository Detection

Before executing Codex commands, check if the working directory is a Git repository:

bash

# Check Git repository status
git rev-parse --git-dir 2>/dev/null && echo "Git repo: YES" || echo "Git repo: NO"

•Git repo exists: Use standard commands
•No Git repo: Add --skip-git-repo-check flag (requires user awareness of security implications)

Quick Start

In Git Repository (Standard)

bash

# Basic code review (terminal)
codex "Review this code for bugs"

# Non-interactive mode (Claude Code/CI)
codex exec -s read-only "Review this code for bugs"

# With specific model and reasoning effort
codex exec -s read-only -m gpt-5.2-codex -c model_reasoning_effort=high "Deep analysis"

# With image input
codex exec -s read-only -i screenshot.png "What's shown here?"

Outside Git Repository

bash

# IMPORTANT: --skip-git-repo-check required for non-Git directories
# Ask user permission before using this flag

codex exec --skip-git-repo-check -s read-only "Review this code for bugs"

# With options
codex exec --skip-git-repo-check -s read-only -m gpt-5.2-codex "Deep analysis"

Session Resume (Special Syntax)

bash

# IMPORTANT: Options must come BEFORE 'resume' subcommand
# SESSION_ID is from previous command output (e.g., 019ae3a3-f1cf-7dc1-8eee-8f424ae7a6f0)

# In Git repository
codex exec -s read-only resume [SESSION_ID] "Continue the analysis"

# Outside Git repository
codex exec --skip-git-repo-check -s read-only resume [SESSION_ID] "Continue the analysis"

Reference Documentation

•Commands Reference - codex, resume, apply, input/output patterns
•Options Reference - Models, sandbox, reasoning effort, approval modes
•Examples - Code review, security analysis, automation scripts

Available Models

Full model details: See Options Reference

Model	Best For
`gpt-5.2-codex`	Complex analysis, critical systems (recommended)
`gpt-5.2`	General AI tasks, multi-domain
`gpt-5.1-codex-max`	Security audits, architecture review
`gpt-5.1-codex-mini`	Quick checks, batch operations

Reasoning Effort

Usage examples: See Options Reference

Level	Use Case
`low`	Simple checks, syntax review
`medium`	Standard code review (default)
`high`	Security audits, complex logic
`xhigh`	Critical systems, exhaustive analysis

Sandbox Modes

Mode	Description
`read-only`	Cannot modify files (safest, recommended)
`workspace-write`	Can modify workspace files
`danger-full-access`	Full system access (use sparingly)

Key Options

Full options list: See Options Reference

Common Patterns

Full examples: See Examples for detailed patterns

Essential Patterns

bash

# Code review (Claude Code/CI)
codex exec -s read-only "Review: $(cat src/auth.js)"

# Maximum depth analysis
codex exec -m gpt-5.2-codex -c model_reasoning_effort=xhigh -s read-only "Security audit"

# Session continuity
codex exec -s read-only resume [SESSION_ID] "Continue analysis"

# Cross-directory
codex exec -C ./backend --add-dir ./frontend -s read-only "Review API"

# Non-Git directory (ask user first)
codex exec --skip-git-repo-check -s read-only "Analyze code"

Platform-Specific Notes

Windows Limitations

Issue	Description	Workaround
`-C` with absolute paths	`cwd is not absolute` error with Windows paths like `C:\path`	Use relative paths (`./subdir`) or run from target directory
Path separators	Backslashes may cause issues	Use forward slashes (`/`) in paths

bash

# AVOID on Windows:
codex exec -C C:\Projects\myapp -s read-only "analyze"

# USE instead:
cd C:\Projects\myapp && codex exec -s read-only "analyze"
# OR use relative paths:
codex exec -C ./myapp -s read-only "analyze"

Error Handling

Error recovery patterns: See Examples

Error	Cause	Solution
`stdin is not a terminal`	Using `codex` in non-TTY	Use `codex exec`
`Not inside a trusted directory`	Not in Git repo	Ask user, then use `--skip-git-repo-check`
`invalid value for '--ask-for-approval'`	Invalid approval value	Use: `untrusted`, `on-failure`, `on-request`, `never`
`unexpected argument` after `resume`	Options after `resume`	Place options BEFORE `resume` subcommand
`cwd is not absolute`	Windows absolute path	Use relative paths or `cd` first
`No prompt provided via stdin`	Empty prompt	Ensure prompt string is not empty

Timeout Configuration

Task Type	Recommended Timeout	Claude Code Tool
Quick checks	2 minutes	`timeout: 120000`
Standard review	5 minutes	`timeout: 300000`
Deep analysis	10 minutes	`timeout: 600000`

Recommendation: Use timeout: 600000 for all Codex exec commands (model_reasoning_effort=high/xhigh can take 3-7 minutes).

Best Practices

•Use codex exec in Claude Code and CI environments (non-TTY)
•Default to -s read-only for all review tasks
•Match model + reasoning effort to task complexity
•Use resume to maintain session context
•Use --add-dir for cross-project context
•Use --full-auto only in controlled environments
•Ask user before --skip-git-repo-check - explain implications
•Check valid approval values - only use untrusted/on-failure/on-request/never
•Set 10-minute timeout for all Codex exec commands (timeout: 600000)