codex

name	codex
description	Use when the user asks about OpenAI Codex CLI (codex, codex exec, codex resume, codex review, codex cloud), wants to run code analysis, refactoring, or automated editing via Codex, needs help configuring AGENTS.md, config.toml, MCP servers, Skills, or Automations, or asks about Codex best practices, approval modes, sandboxing, or multi-agent workflows.

Codex Skill Guide

Models

Model	Notes
gpt-5.4	Default & recommended — frontier reasoning + coding
gpt-5.3-codex	Strong coding focus
gpt-5.3-codex-spark	Extra fast; ChatGPT Pro only (research preview)

• Set default: model = "gpt-5.4" in ~/.codex/config.toml
• Override per-run: codex -m gpt-5.4 or /model in-session
• Reasoning effort: --config model_reasoning_effort="high|medium|low" (or set in config)
  • Low → fast, well-scoped tasks; Medium/High → complex changes or debugging; Extra High → long agentic tasks

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Best Practices

Effective prompting

A strong prompt includes four things:

1. Goal — what to change or build
2. Context — relevant files, folders, docs, errors (use @file mentions)
3. Constraints — standards, architecture, conventions to follow
4. Done when — tests pass, behavior changes, bug no longer reproduces

Plan before complex tasks

• Plan mode: toggle with /plan or Shift+Tab — Codex gathers context, asks questions, builds a plan before coding
• Interview mode: ask Codex to question you first to sharpen fuzzy requirements
• PLANS.md template: configure an execution-plan template for multi-step work

AGENTS.md — durable guidance

AGENTS.md loads into context automatically; encode how your team wants Codex to work.

A good AGENTS.md covers:

• Repo layout and important directories
• How to run, build, test, and lint the project
• Engineering conventions and PR expectations
• Constraints / do-not rules
• Definition of done

Layering precedence (most specific wins):

• ~/.codex/AGENTS.md — personal global defaults
• <repo>/AGENTS.md — shared repo standards
• <repo>/subdir/AGENTS.md — local rules for a subtree

Use /init in the CLI to scaffold a starter AGENTS.md, then edit it for your team.

When Codex makes the same mistake twice, ask for a retrospective and update AGENTS.md.

Skills & Automations

• Skills: package a repeatable workflow into a SKILL.md file; stored in $HOME/.agents/skills (personal) or .agents/skills/ in a repo (shared)
• Use $skill-creator to scaffold a new skill; $skill-installer to install it
• Automations: schedule stable skills to run in the background via the Codex app Automations tab
• Rule of thumb: if you keep reusing the same prompt → skill; if the skill is stable and predictable → automation

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Interactive Mode

codex                        # Launch TUI
codex "explain this codebase" # Launch with initial prompt
codex -i screenshot.png "Fix this error"  # Attach image(s)
codex --cd <path>            # Set working directory
codex --add-dir ../backend   # Grant extra writable root(s)
codex --full-auto            # workspace-write sandbox + on-request approvals

In-session shortcuts:

• @ → fuzzy file search; Tab/Enter to insert path
• Enter while running → inject instructions mid-turn; Tab → queue follow-up
• !command → run a local shell command inline
• Esc Esc (empty composer) → edit previous message; continue pressing to walk back
• Ctrl+G → open $VISUAL/$EDITOR for long prompts
• Up/Down → navigate draft history
• /clear or Ctrl+L → clear screen; /copy → copy latest output
• /permissions → switch approval mode live
• /theme → pick syntax highlight theme
• /model → switch model mid-session
• Ctrl+C or /exit → close session

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Session Management

# Resume interactive sessions
codex resume                 # Picker of recent sessions
codex resume --last          # Most recent session (current dir)
codex resume --last --all    # Most recent session (any dir)
codex resume <SESSION_ID>    # Specific session

# Fork a session (preserves original transcript)
codex fork                   # Picker
codex fork --last            # Fork most recent

# Non-interactive resume
codex exec resume --last "Follow-up instruction"
codex exec resume <ID> "Follow-up instruction"

Session controls (slash commands):

• /resume — reopen a saved conversation
• /fork — branch into a new thread
• /compact — summarize long context (Codex also does this automatically)
• /agent — switch between active agents in multi-agent mode
• /status — inspect current session state

Keep one thread per coherent unit of work. Fork only when work truly branches.

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Local Code Review

# Type /review inside an interactive session, or:
codex exec "/review"

Review presets (no working-tree modifications):

• Review against base branch — diffs to merge base, highlights risks before PR
• Review uncommitted changes — staged + unstaged + untracked
• Review a commit — pick a SHA from recent list
• Custom review instructions — e.g. "Focus on accessibility regressions"

Each review appears as its own turn; re-run as code evolves. Reference a code_review.md from AGENTS.md for consistent team review behavior.

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Non-Interactive / Scripted Runs (codex exec)

codex exec "fix the CI failure"
codex e "summarize open bugs"                    # short alias

# Pipe prompt from stdin
echo "Refactor auth module" | codex exec -

# JSON output for scripting
codex exec --json "task"

# Capture final message to file
codex exec --json --output-last-message result.md "task"

# Resume non-interactive
codex exec resume --last "Continue the refactor"

Key exec flags:

Flag	Purpose
--sandbox/-s read-only|workspace-write|danger-full-access	Sandbox policy
--full-auto	workspace-write + on-request approvals
--yolo / --dangerously-bypass-approvals-and-sandbox	No approvals or sandbox — isolated runner only
--skip-git-repo-check	Allow running outside a git repo
--ephemeral	No session files persisted to disk
--output-schema <path>	Validate final response against JSON Schema
--json	Newline-delimited JSON events
--output-last-message/-o <path>	Write final assistant message to file
--cd/-C <path>	Set workspace root
--add-dir <path>	Grant extra writable root

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Approval & Sandbox Modes

Approval (--ask-for-approval):

• on-request — interactive default; Codex pauses for confirmation before risky actions
• untrusted — stricter; prompts more often
• never — non-interactive / CI runs

Sandbox (--sandbox):

• read-only — browse only, no edits/exec
• workspace-write — read/edit/run within workspace (default in --full-auto)
• danger-full-access — full machine access; use inside an isolated VM only

Toggle live with /permissions in an interactive session.

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Web Search

codex --search               # Live search for one run

Config options in ~/.codex/config.toml:

web_search = "live"          # always live
web_search = "cached"        # default (pre-indexed, lower injection risk)
web_search = "disabled"      # off

[features]
web_search_request = true

[sandbox_workspace_write]
network_access = true

---

Codex Cloud

codex cloud                              # Interactive picker
codex cloud exec --env ENV_ID "task"     # Submit task directly
codex cloud exec --env ENV_ID --attempts 3 "task"  # Best-of-N (1–4)
codex cloud list                         # Recent tasks
codex cloud list --env ENV_ID --json     # Filtered + machine-readable
codex apply <TASK_ID>                    # Apply cloud task diff locally

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MCP (Model Context Protocol)

codex mcp list               # List configured servers
codex mcp add <name> -- <cmd> [args]   # Register stdio server
codex mcp add <name> --url https://...  # Register streamable HTTP server
codex mcp remove <name>
codex mcp login <name>       # OAuth for HTTP servers
codex mcp-server             # Run Codex itself as an MCP server (stdio)

Config in ~/.codex/config.toml:

[mcp_servers.my_tool]
command = "npx"
args = ["-y", "@my/tool-server"]

[mcp_servers.my_http_tool]
url = "https://api.example.com/mcp"
bearer_token_env_var = "MY_TOOL_API_KEY"

Add MCP servers only when they remove a real manual loop. Start with 1–2 tools.

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Multi-Agent (Experimental)

• Enable via codex features enable unified_exec or [agents] section in config.toml
• Use /agent to switch between active agent threads
• Offload bounded subtasks (exploration, tests, triage) to subagents; keep the main agent focused
• Configure roles, parallelism, and routing under [agents] in config.toml

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Shell Completions

codex completion zsh          # Print zsh completion script

# Add to ~/.zshrc:
autoload -Uz compinit && compinit
eval "$(codex completion zsh)"

Supports: bash, zsh, fish, power-shell, elvish

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Feature Flags

codex features list
codex features enable unified_exec
codex features disable shell_snapshot

Or per-run: codex --enable <feature> / --disable <feature>

Common flags: web_search_request, streamable_shell, unified_exec, rmcp_client, apply_patch_freeform, view_image_tool

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CLI Reference

Global flags (apply to all commands)

Flag	Type	Description
PROMPT	string	Initial prompt (optional)
--image/-i	path[,...]	Attach image file(s)
--model/-m	string	Override model
--oss	bool	Use local OSS provider (Ollama)
--sandbox/-s	enum	Sandbox policy
--ask-for-approval/-a	enum	Approval trigger
--full-auto	bool	workspace-write + on-request shortcut
--yolo	bool	Bypass all approvals/sandbox
--cd/-C	path	Set working directory
--profile/-p	string	Load named config profile
--search	bool	Enable live web search
--add-dir	path	Grant extra writable root (repeatable)
--enable/--disable	feature	Toggle feature flag
--config/-c	key=value	Inline config override (repeatable)
--no-alt-screen	bool	Disable TUI alternate screen

Command overview

Command	Notes
codex	Interactive TUI
codex exec / codex e	Non-interactive run; + resume subcommand
codex resume	Continue interactive session
codex fork	Fork interactive session
codex apply	Apply Codex Cloud diff locally
codex cloud / codex cloud exec	Cloud task management
codex login / logout / login status	Authentication
codex mcp	Manage MCP servers
codex mcp-server	Run Codex as MCP server
codex completion	Generate shell completion scripts
codex features	Manage feature flags
codex sandbox	Run commands in Codex sandbox (macOS/Linux)
codex app	Launch Codex Desktop (macOS)
codex execpolicy	Evaluate execpolicy rule files

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config.toml Reference

Location: ~/.codex/config.toml (shared by CLI + IDE)

# Core
model = "gpt-5.4"
model_provider = "openai"
approval_policy = "on-request"          # on-request | untrusted | never
sandbox_mode = "workspace-write"        # read-only | workspace-write | danger-full-access
model_reasoning_effort = "medium"       # high | medium | low
model_reasoning_summary = "concise"
model_verbosity = "normal"
model_context_window = 200000
model_max_output_tokens = 32768

# TUI
[tui]
theme = "Monokai Extended"
alternate_screen = true

# Web search
web_search = "cached"                   # live | cached | disabled

# Shell environment policy (prevent secret leakage)
[shell_environment_policy]
inherit = "none"
include_only = ["PATH", "HOME", "LANG"]
# or: exclude = ["*_KEY", "*_SECRET", "*_TOKEN"]

# Profiles
[profiles.ci]
model = "gpt-5.3-codex"
sandbox_mode = "read-only"
approval_policy = "never"

# Feature flags

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Config precedence: CLI flags > profile > repo .codex/config.toml > ~/.codex/config.toml > defaults

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Assistant Playbook

When helping a user run a Codex task:

1. Clarify in one prompt: confirm model (gpt-5.4 default), reasoning effort (high|medium|low), and target directory
2. Choose sandbox: default --sandbox read-only for analysis; workspace-write when edits are needed; never suggest danger-full-access without explicit user approval
3. Build the command with:
   • -m <model> if non-default
   • --config model_reasoning_effort=<effort> if specified
   • --sandbox <mode> appropriate for task
   • --skip-git-repo-check when running outside a git repo
   • -C <dir> to set working directory
   • Append 2>/dev/null to codex exec unless user wants stderr
4. For resume: codex exec resume --last "follow-up" 2>/dev/null — no extra flags unless user requests
5. Run, then summarize stdout; include stderr only if relevant or requested
6. After completion: remind user they can run codex resume to continue interactively
7. Confirm next steps: ask whether to resume, adjust, or close; restate model/effort/sandbox in summary
8. On non-zero exit: stop and ask before retrying; never retry high-impact flags automatically
9. For high-impact flags (--full-auto, --yolo, --sandbox danger-full-access): explicitly ask for permission and explain the risk first
10. For complex tasks: suggest Plan mode (/plan or Shift+Tab) before implementation

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Common Mistakes to Avoid

• Overloading prompts with rules that belong in AGENTS.md or a skill
• Not specifying build/test commands so Codex can't verify its own work
• Skipping planning for multi-step or ambiguous tasks
• Granting danger-full-access before understanding the workflow
• Running concurrent threads on the same files without git worktrees
• Automating a workflow before it's reliable manually
• Using one long-running thread per project instead of one thread per task
• Treating Codex as a step-by-step tool instead of running it in parallel with other work