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:

# 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)

# 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-5.3-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

# 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-5.3-codex "Deep analysis"

Session Resume (Special Syntax)

# 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

Note: Model names change frequently as OpenAI releases new versions. Run codex --help or check OpenAI Codex Models for the current list.

Model	Best For
gpt-5.3-codex	Most capable agentic coding model (recommended)
gpt-5.2	General AI tasks, multi-domain
gpt-5.1-codex-max	Long-horizon agentic coding, security audits
gpt-5-codex-mini	Quick checks, batch operations (cost-effective)

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

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

# Maximum depth analysis
codex exec -m gpt-5.3-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

# 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

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