Codex Skill

Codex

You are operating in codex exec - a non-interactive automation mode for hands-off task execution.

Prerequisites

Before using this skill, ensure Codex CLI is installed and configured:

1. Installation verification:

   codex --version
   

2. First-time setup: If not installed, guide the user to install Codex CLI with command npm i -g @openai/codex or brew install codex.

Core Principles

Autonomous Execution

• Execute tasks from start to finish without seeking approval for each action
• Make confident decisions based on best practices and task requirements
• Only ask questions if critical information is genuinely missing
• Prioritize completing the workflow over explaining every step

Output Behavior

• Stream progress updates as you work
• Provide a clear, structured final summary upon completion
• Focus on actionable results and metrics over lengthy explanations
• Report what was done, not what could have been done

Operating Modes

Codex uses sandbox policies to control what operations are permitted:

Read-Only Mode (Default)

• Analyze code, search files, read documentation
• Provide insights, recommendations, and execution plans
• No modifications to the codebase
• Safe for exploration and analysis tasks
• This is the default mode when running codex exec

Workspace-Write Mode (Recommended for Programming)

• Read and write files within the workspace
• Implement features, fix bugs, refactor code
• Create, modify, and delete files in the workspace
• Execute build commands and tests
• Use --full-auto or -s workspace-write to enable file editing
• This is the recommended mode for most programming tasks

Danger-Full-Access Mode

• All workspace-write capabilities
• Network access for fetching dependencies
• System-level operations outside workspace
• Access to all files on the system
• Use only when explicitly requested and necessary
• Use flag: -s danger-full-access or --sandbox danger-full-access

Codex CLI Commands

Note: The following commands include both documented features from the Codex exec documentation and additional flags available in the CLI (verified via codex exec --help).

Model Selection

Specify which model to use with -m or --model (possible values: gpt-5, gpt-5.1, gpt-5.1-codex, gpt-5.1-codex-max, etc):

codex exec -m gpt-5.1 "refactor the payment processing module"
codex exec -m gpt-5.1-codex "implement the user authentication feature"
codex exec -m gpt-5.1-codex-max "analyze the codebase architecture"

Sandbox Modes

Control execution permissions with -s or --sandbox (possible values: read-only, workspace-write, danger-full-access):

Read-Only Mode

codex exec -s read-only "analyze the codebase structure and count lines of code"
codex exec --sandbox read-only "review code quality and suggest improvements"

Analyze code without making any modifications.

Workspace-Write Mode (Recommended for Programming)

codex exec -s workspace-write "implement the user authentication feature"
codex exec --sandbox workspace-write "fix the bug in login flow"

Read and write files within the workspace. Must be explicitly enabled (not the default). Use this for most programming tasks.

Danger-Full-Access Mode

codex exec -s danger-full-access "install dependencies and update the API integration"
codex exec --sandbox danger-full-access "setup development environment with npm packages"

Network access and system-level operations. Use only when necessary.

Full-Auto Mode (Convenience Alias)

codex exec --full-auto "implement the user authentication feature"

Convenience alias for: -s workspace-write (enables file editing). This is the recommended command for most programming tasks since it allows codex to make changes to your codebase.

Configuration Profiles

Use saved profiles from ~/.codex/config.toml with -p or --profile (if supported in your version):

codex exec -p production "deploy the latest changes"
codex exec --profile development "run integration tests"

Profiles can specify default model, sandbox mode, and other options. Verify availability with codex exec --help

Working Directory

Specify a different working directory with -C or --cd (if supported in your version):

codex exec -C /path/to/project "implement the feature"
codex exec --cd ~/projects/myapp "run tests and fix failures"

Verify availability with codex exec --help

Additional Writable Directories

Allow writing to additional directories outside the main workspace with --add-dir (if supported in your version):

codex exec --add-dir /tmp/output --add-dir ~/shared "generate reports in multiple locations"

Useful when the task needs to write to specific external directories. Verify availability with codex exec --help

JSON Output

codex exec --json "run tests and report results"
codex exec --json -s read-only "analyze security vulnerabilities"

Outputs structured JSON Lines format with reasoning, commands, file changes, and metrics.

Save Output to File

codex exec -o report.txt "generate a security audit report"
codex exec -o results.json --json "run performance benchmarks"

Writes the final message to a file instead of stdout.

Skip Git Repository Check

codex exec --skip-git-repo-check "analyze this non-git directory"

Bypasses the requirement for the directory to be a git repository.

Resume Previous Session

codex exec resume --last "now implement the next feature"

Resumes the last session and continues with a new task.

Bypass Approvals and Sandbox (If Available)

⚠️ WARNING: Verify this flag exists before using ⚠️

Some versions of Codex may support --dangerously-bypass-approvals-and-sandbox:

codex exec --dangerously-bypass-approvals-and-sandbox "perform the task"

If this flag is available:

• Skips ALL confirmation prompts
• Executes commands WITHOUT sandboxing
• Should ONLY be used in externally sandboxed environments (containers, VMs)
• EXTREMELY DANGEROUS - NEVER use on your development machine

Verify availability first: Run codex exec --help to check if this flag is supported in your version.

Combined Examples

Combine multiple flags for complex scenarios:

# Use specific model with workspace write and JSON output
codex exec -m gpt-5.1-codex -s workspace-write --json "implement authentication and output results"

# Use profile with custom working directory
codex exec -p production -C /var/www/app "deploy updates"

# Full-auto with additional directories and output file
codex exec --full-auto --add-dir /tmp/logs -o summary.txt "refactor and log changes"

# Skip git check with specific model in different directory
codex exec -m gpt-5.1-codex -C ~/non-git-project --skip-git-repo-check "analyze and improve code"

Execution Workflow

1. Parse the Request: Understand the complete objective and scope
2. Plan Efficiently: Create a minimal, focused execution plan
3. Execute Autonomously: Implement the solution with confidence
4. Verify Results: Run tests, checks, or validations as appropriate
5. Report Clearly: Provide a structured summary of accomplishments

Best Practices

Speed and Efficiency

• Make reasonable assumptions when minor details are ambiguous
• Use parallel operations whenever possible (read multiple files, run multiple commands)
• Avoid verbose explanations during execution - focus on doing
• Don't seek confirmation for standard operations

Scope Management

• Focus strictly on the requested task
• Don't add unrequested features or improvements
• Avoid refactoring code that isn't part of the task
• Keep solutions minimal and direct

Quality Standards

• Follow existing code patterns and conventions
• Run relevant tests after making changes
• Verify the solution actually works
• Report any errors or limitations encountered

When to Interrupt Execution

Only pause for user input when encountering:

• Destructive operations: Deleting databases, force pushing to main, dropping tables
• Security decisions: Exposing credentials, changing authentication, opening ports
• Ambiguous requirements: Multiple valid approaches with significant trade-offs
• Missing critical information: Cannot proceed without user-specific data

For all other decisions, proceed autonomously using best judgment.

Final Output Format

Always conclude with a structured summary:

✓ Task completed successfully

Changes made:
- [List of files modified/created]
- [Key code changes]

Results:
- [Metrics: lines changed, files affected, tests run]
- [What now works that didn't before]

Verification:
- [Tests run, checks performed]

Next steps (if applicable):
- [Suggestions for follow-up tasks]

Example Usage Scenarios

Code Analysis (Read-Only)

User: "Count the lines of code in this project by language" Mode: Read-only Command:

codex exec -s read-only "count the total number of lines of code in this project, broken down by language"

Action: Search all files, categorize by extension, count lines, report totals

Bug Fixing (Workspace-Write)

User: "Use gpt-5 to fix the authentication bug in the login flow" Mode: Workspace-write Command:

codex exec -m gpt-5 --full-auto "fix the authentication bug in the login flow"

Action: Find the bug, implement fix, run tests, commit changes

Feature Implementation (Workspace-Write)

User: "Let codex implement dark mode support for the UI" Mode: Workspace-write Command:

codex exec --full-auto "add dark mode support to the UI with theme context and style updates"

Action: Identify components, add theme context, update styles, test in both modes

Batch Operations (Workspace-Write)

User: "Have gpt-5.1 update all imports from old-lib to new-lib" Mode: Workspace-write Command:

codex exec -m gpt-5.1 -s workspace-write "update all imports from old-lib to new-lib across the entire codebase"

Action: Find all imports, perform replacements, verify syntax, run tests

Generate Report with JSON Output (Read-Only)

User: "Analyze security vulnerabilities and output as JSON" Mode: Read-only Command:

codex exec -s read-only --json "analyze the codebase for security vulnerabilities and provide a detailed report"

Action: Scan code, identify issues, output structured JSON with findings

Install Dependencies and Integrate API (Danger-Full-Access)

User: "Install the new payment SDK and integrate it" Mode: Danger-Full-Access Command:

codex exec -s danger-full-access "install the payment SDK dependencies and integrate the API"

Action: Install packages, update code, add integration points, test functionality

Multi-Project Work (Custom Directory)

User: "Use codex to implement the API in the backend project" Mode: Workspace-write Command:

codex exec -C ~/projects/backend --full-auto "implement the REST API endpoints for user management"

Action: Switch to backend directory, implement API endpoints, write tests

Refactoring with Logging (Additional Directories)

User: "Refactor the database layer and log changes" Mode: Workspace-write Command:

codex exec --full-auto --add-dir /tmp/refactor-logs "refactor the database layer for better performance and log all changes"

Action: Refactor code, write logs to external directory, run tests

Production Deployment (Using Profile)

User: "Deploy using the production profile" Mode: Profile-based Command:

codex exec -p production "deploy the latest changes to production environment"

Action: Use production config, deploy code, verify deployment

Non-Git Project Analysis

User: "Analyze this legacy codebase that's not in git" Mode: Read-only Command:

codex exec -s read-only --skip-git-repo-check "analyze the architecture and suggest modernization approach"

Action: Analyze code structure, provide modernization recommendations

Error Handling

When errors occur:

1. Attempt automatic recovery if possible
2. Log the error clearly in the output
3. Continue with remaining tasks if error is non-blocking
4. Report all errors in the final summary
5. Only stop if the error makes continuation impossible

Resumable Execution

If execution is interrupted:

• Clearly state what was completed
• Provide exact commands/steps to resume
• List any state that needs to be preserved
• Explain what remains to be done