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 claude -r 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 selection -s, --sandbox read-only|workspace-write|danger-full-access -a, --ask-for-approval

untrusted|on-failure|on-request|never -c, --config Override config -C, --cd

Working directory -i, --image Attach image(s) -p, --profile Config profile --full-auto Low-friction mode --yolo Bypass all safety (DANGEROUS) --search Enable web search --add-dir Grant additional write access --enable Enable feature flag --disable Disable feature flag --oss Use local OSS model Claude Code CLI (Anthropic) Installation npm install -g @anthropic-ai/claude-code Authentication claude

First run prompts login

claude setup-token

Set up long-lived token

Requires Claude Pro/Max subscription OR API key

Core Commands claude - Interactive Mode claude

Start REPL

claude "explain this project"

With prompt

claude -c

Continue last conversation

claude -r "session-name"

Resume by name/ID

claude --model opus

Select model

claude --chrome

Enable Chrome integration

claude --ide

Auto-connect to IDE

claude -p - Print Mode (Non-Interactive) claude -p "explain this function"

Query and exit

cat file | claude -p "explain"

Process piped input

claude -p --output-format json "q"

JSON output

claude -p --output-format stream-json "q"

Streaming JSON

claude -p --max-turns 3 "task"

Limit agent turns

claude -p --max-budget-usd 5 "task"

Spending limit

claude -p --json-schema '{...}' "q"

Validate output schema

claude mcp - MCP Server Management claude mcp list

List servers

claude mcp get < name

Server details

claude mcp add < name

< cmd

Add stdio server

claude mcp add -t http < name

< url

Add HTTP server

claude mcp add -e KEY = val < name

-- cmd

With env vars

claude mcp add -H "Auth: Bearer x" < name

< url

With headers

claude mcp add -s project < name

< cmd

Project scope

claude mcp remove < name

Remove server

claude mcp serve

Run as MCP server

claude mcp add-from-claude-desktop

Import from desktop app

claude mcp reset-project-choices

Reset approvals

claude plugin - Plugin Management claude plugin list

List plugins

claude plugin install < name

Install plugin

claude plugin install < name

@marketplace

From specific marketplace

claude plugin uninstall < name

Remove plugin

claude plugin enable < name

Enable disabled plugin

claude plugin disable < name

Disable plugin

claude plugin update < name

Update plugin

claude plugin validate < path

Validate manifest

claude plugin marketplace

Manage marketplaces

claude update - Self-Update claude update

Check and install updates

claude doctor - Diagnostics claude doctor

Check health/issues

claude install - Native Build claude install

Install native build

claude install stable

Specific version

claude install latest

Latest version

Slash Commands (Interactive) Command Purpose /init Generate CLAUDE.md /clear Reset context /compact Summarize conversation /bug Report issues /doctor Run diagnostics /model Switch model /config View/edit settings /permissions Manage permissions /memory View/edit memory /project: Project-specific commands /user: User-specific commands Custom Commands Create .claude/commands/fix-issue.md : Fix GitHub issue #$ARGUMENTS 1. Read the issue details 2. Identify the problem 3. Implement the fix 4. Write tests 5. Create a commit Usage: /project:fix-issue 1234 Configuration User settings ( ~/.claude/settings.json ): { "model" : "claude-sonnet-4-5-20250929" , "verbose" : false , "theme" : "dark" } Project settings ( .claude/settings.json ): { "allowedTools" : [ "Bash(git:)" , "Read" , "Edit" ] , "disallowedTools" : [ "Bash(rm:)" ] } CLI Flags Core -p, --print Non-interactive mode -c, --continue Continue last conversation -r, --resume Resume specific session -v, --version Show version Model & Config --model sonnet|opus|haiku or full name --fallback-model Fallback when overloaded --settings Load settings JSON --setting-sources user,project,local --session-id Use specific session ID System Prompt --system-prompt Replace default prompt --append-system-prompt Append to default --system-prompt-file Replace with file (print only) --append-system-prompt-file Replace with file (print only) Agent & Tools --agent Specify agent --agents Define custom subagents --tools Restrict built-in tools --allowedTools Auto-approve tools --disallowedTools Remove tools from context Permissions --permission-mode acceptEdits|bypassPermissions|default|delegate|dontAsk|plan --dangerously-skip-permissions Skip all prompts (DANGEROUS) --allow-dangerously-skip-permissions Enable bypass option Output --output-format text|json|stream-json --input-format text|stream-json --include-partial-messages Include streaming chunks --verbose Verbose logging --debug [FILTER] Debug mode with filtering Advanced --max-turns Limit agent turns (print only) --max-budget-usd Spending limit (print only) --json-schema Validate JSON output --chrome / --no-chrome Chrome integration --ide IDE auto-connect --fork-session Create new session on resume --no-session-persistence Don't save session --add-dir Additional directories --plugin-dir Load plugins --disable-slash-commands Disable all skills --mcp-config MCP server configs --strict-mcp-config Only use specified MCP --betas Beta API headers Custom Subagents claude --agents '{ "reviewer": { "description": "Code reviewer. Use after changes.", "prompt": "You are a senior code reviewer...", "tools": ["Read", "Grep", "Glob"], "model": "sonnet" } }' Common Patterns & Edge Cases CI/CD Integration Codex in GitHub Actions: - name : Run Codex run : | echo "${{ secrets.OPENAI_API_KEY }}" | codex login --with-api-key codex exec --json -o result.txt "fix linting errors" Claude in CI: - name : Run Claude env : ANTHROPIC_API_KEY : $ { { secrets.ANTHROPIC_API_KEY } } run : | claude -p --output-format json "review this PR" > review.json Handling Rate Limits Codex: Automatic backoff built-in. Claude: Use --fallback-model : claude -p --fallback-model haiku "quick task" Working with Large Codebases

Codex: Use /compact to free context

In session: /compact

Claude: Use /compact or start fresh

claude --no-session-persistence -p "analyze src/" Multi-Directory Access

Codex

codex --add-dir .. /shared-lib --add-dir .. /config

Claude

claude --add-dir .. /shared-lib .. /config Structured Output Codex: codex exec --output-schema schema.json "generate API spec" Claude: claude -p --json-schema '{"type":"object","properties":{"name":{"type":"string"}}}' "extract data" Image Input Codex: codex -i screenshot.png "explain this UI" codex -i img1.png -i img2.png "compare these" Claude:

Via file reference in prompt

claude "analyze the image at ./screenshot.png" Session Forking

Codex: /fork in session

Claude

claude -r "session-id" --fork-session "try alternative approach" MCP Server Debugging Codex: codex mcp list --json | jq . Claude: claude --debug "mcp" --mcp-config ./mcp.json Troubleshooting Authentication Issues Problem Codex Claude Not logged in codex login status claude doctor Token expired codex logout && codex login claude setup-token API key issues Check OPENAI_API_KEY Check ANTHROPIC_API_KEY Sandbox Issues Problem Solution Permission denied Use --add-dir for specific directories Can't run commands Check sandbox mode, use workspace-write Network blocked Sandbox may block network; use danger-full-access carefully MCP Server Issues Problem Solution Server not found Check mcp list , verify installation Connection failed Check server logs, verify URL/command Auth required Use mcp login (Codex) or add headers (Claude) Performance Issues Problem Solution Slow responses Use lighter model (gpt-4.1-mini / haiku) Context overflow Use /compact to summarize High costs Set --max-budget-usd (Claude) Best Practices Start with read-only for exploration, escalate as needed Use sessions - resume work instead of starting fresh Create AGENTS.md/CLAUDE.md for project-specific instructions Leverage MCP servers for external integrations Use structured output in CI/CD for parsing Set spending limits with --max-budget-usd Review diffs before applying ( /diff , codex cloud diff ) Commit checkpoints before major changes