/ai-coding-agents

name: ai-coding-agents
description: Comprehensive guide for using Codex CLI (OpenAI) and Claude Code CLI (Anthropic) - AI-powered coding agents. Use when orchestrating CLI commands, automating tasks, configuring agents, or troubleshooting issues.

AI Coding Agents Skill

Expert knowledge for Codex CLI and Claude Code CLI — the two leading AI coding agents.

**Note:** This skill documents both tools for reference. VMark development primarily uses **Claude Code CLI**. The Codex CLI sections are retained for completeness and cross-tool workflows.

When to Use

• Orchestrating complex coding tasks via CLI
• Configuring MCP servers for either tool
• Setting up automation pipelines (CI/CD)
• Troubleshooting authentication or sandbox issues
• Comparing capabilities between agents
• Custom agent/subagent configuration

Quick Reference

Starting Sessions

| Task | Codex CLI | Claude Code CLI | |------|-----------|-----------------| | Interactive session | `codex` | `claude` | | With prompt | `codex "fix the bug"` | `claude "fix the bug"` | | Non-interactive | `codex exec "task"` | `claude -p "task"` | | Resume last | `codex resume --last` | `claude -c` | | Resume by ID | `codex resume <id>` | `claude -r <id>` |

Safety Modes

| Mode | Codex CLI | Claude Code CLI | |------|-----------|-----------------| | Read-only | `-s read-only` | `--permission-mode plan` | | Workspace write | `-s workspace-write` | (default) | | Full access | `-s danger-full-access` | `--dangerously-skip-permissions` | | Auto mode | `--full-auto` | `--permission-mode default` | | YOLO mode | `--yolo` | `--dangerously-skip-permissions` |

Model Selection

| Task | Codex CLI | Claude Code CLI | |------|-----------|-----------------| | Select model | `-m gpt-5-codex` | `--model opus` | | Use local OSS | `--oss` | N/A | | Fallback model | N/A | `--fallback-model sonnet` |

---

Codex CLI (OpenAI)

Installation

npm i -g @openai/codex
# or
brew install --cask codex

Authentication

codex login              # OAuth via ChatGPT
codex login --with-api-key   # Read API key from stdin
codex login status       # Check auth status
codex logout             # Remove credentials

Core Commands

`codex` - Interactive Mode

codex                           # Start TUI
codex "fix all TypeScript errors"  # With initial prompt
codex -i screenshot.png "explain"  # With image
codex --full-auto "refactor"    # Low-friction mode
codex --search "find docs"      # Enable web search

`codex exec` - Non-Interactive

codex exec "write tests"        # Run and exit
codex e "task"                  # Short alias
echo "task" | codex exec -      # From stdin
codex exec --json "task"        # JSONL output
codex exec -o result.txt "task" # Save to file
codex exec --output-schema schema.json "task"  # Validate output

`codex resume` - Continue Sessions

codex resume                    # Interactive picker
codex resume --last             # Most recent
codex resume --all              # Show all (any directory)
codex resume <session-id>       # Specific session
codex resume <id> "continue with this"  # With prompt

`codex review` - Code Review

codex review                    # Review current branch vs main
codex review --uncommitted      # Review uncommitted changes
codex review --base develop     # Against specific branch
codex review --commit abc123    # Review specific commit
codex review "focus on security"  # Custom instructions

`codex apply` - Apply Cloud Task

codex apply <task-id>           # Apply diff from cloud task

`codex cloud` - Cloud Tasks (Experimental)

codex cloud                     # Browse cloud tasks
codex cloud exec "task" --env <env-id>  # Submit task
codex cloud status <task-id>    # Check status
codex cloud diff <task-id>      # Show diff
codex cloud apply <task-id>     # Apply changes

`codex mcp` - MCP Server Management

codex mcp list                  # List servers
codex mcp list --json           # JSON output
codex mcp get <name>            # Server details
codex mcp add <name> -- npx my-server   # Add stdio server
codex mcp add <name> --url https://... # Add HTTP server
codex mcp add <name> --env API_KEY=xxx -- cmd  # With env vars
codex mcp remove <name>         # Remove server
codex mcp login <name> --scopes read,write  # OAuth for HTTP
codex mcp logout <name>         # Remove OAuth

`codex sandbox` - Run Sandboxed Commands

# macOS
codex sandbox macos -- npm test
codex sandbox seatbelt --full-auto -- ./script.sh

# Linux
codex sandbox linux -- npm test
codex sandbox landlock -- ./script.sh

`codex completion` - Shell Completions

codex completion bash >> ~/.bashrc
codex completion zsh >> ~/.zshrc
codex completion fish > ~/.config/fish/completions/codex.fish

Slash Commands (Interactive)

| Command | Purpose | |---------|---------| | `/model` | Switch model (gpt-5-codex, gpt-5, etc.) | | `/approvals` | Change approval policy | | `/compact` | Summarize conversation, free context | | `/diff` | Show git diff | | `/review` | Analyze working tree | | `/status` | Show config and token usage | | `/mcp` | List available MCP tools | | `/mention` | Attach files | | `/fork` | Branch conversation | | `/resume` | Reopen previous session | | `/new` | Fresh conversation | | `/init` | Create AGENTS.md scaffold | | `/feedback` | Submit logs/diagnostics | | `/quit`, `/exit` | Exit CLI |

Configuration (`~/.codex/config.toml`)

model = "gpt-5-codex"
approval_policy = "on-request"

[sandbox]
mode = "workspace-write"

[features]
web_search = true

[profiles.ci]
model = "gpt-4.1"
approval_policy = "never"

Global Flags

-m, --model <MODEL>          Model selection
-s, --sandbox <MODE>         read-only|workspace-write|danger-full-access
-a, --ask-for-approval <P>   untrusted|on-failure|on-request|never
-c, --config <KEY=VA