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What are Skills?

Skills are modular, self-contained folders that extend Codex’s capabilities by providing specialized knowledge, workflows, and tools. Think of them as “onboarding guides” for specific domains or tasks—they transform Codex from a general-purpose agent into a specialized agent equipped with procedural knowledge.

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What Skills Provide

Skills can include:
  1. Specialized workflows - Multi-step procedures for specific domains
  2. Tool integrations - Instructions for working with specific file formats or APIs
  3. Domain expertise - Company-specific knowledge, schemas, business logic
  4. Bundled resources - Scripts, references, and assets for complex and repetitive tasks

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How Skills Work

Skills use a three-level progressive disclosure system to manage context efficiently:
1

Metadata (name + description)

Always loaded in context (~100 words). This helps Codex determine when to use the skill.
2

SKILL.md body

Loaded when the skill triggers (less than 5k words). Contains instructions and workflows.
3

Bundled resources

Loaded as needed by Codex. Scripts can be executed without reading into context.

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Skill Structure

Every skill follows this structure: 
skill-name/
├── SKILL.md (required)
│   ├── YAML frontmatter metadata (required)
│   │   ├── name: (required)
│   │   └── description: (required)
│   └── Markdown instructions (required)
├── agents/ (recommended)
│   └── openai.yaml - UI metadata for skill lists
└── Bundled Resources (optional)
    ├── scripts/          - Executable code (Python/Bash/etc.)
    ├── references/       - Documentation loaded as needed
    └── assets/           - Files used in output (templates, icons, etc.)

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SKILL.md (Required)

The main skill file consists of:
  • Frontmatter (YAML): Contains name and description fields. These are critical—Codex reads them to determine when to use the skill.
  • Body (Markdown): Instructions and guidance for using the skill. Only loaded after the skill triggers.
The description in the frontmatter is the primary triggering mechanism. Include both what the skill does and specific triggers/contexts for when to use it.

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Bundled Resources (Optional)

Scripts

Executable code for tasks requiring deterministic reliability. Token efficient and may be executed without loading into context.Example: scripts/rotate_pdf.py for PDF rotation

References

Documentation loaded as needed to inform Codex’s process. Keeps SKILL.md lean.Example: references/api_docs.md for API specifications

Assets

Files used in output, not loaded into context.Example: assets/logo.png for brand assets

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Installing Skills

Skills are stored in $CODEX_HOME/skills/ (typically ~/.codex/skills/).

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System Skills (Built-in)

Codex comes with built-in system skills that are automatically installed to $CODEX_HOME/skills/.system/ on startup. These include:
  • skill-creator: Guide for creating effective skills
  • skill-installer: Install skills from GitHub repositories
System skills are updated automatically when you update Codex.

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Installing Additional Skills

Use the built-in skill-installer skill to install additional skills: 
# In Codex, type:
/use skill-installer
"List available skills"
After installing a new skill, restart Codex to pick it up.

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Creating a Skill

Codex includes a built-in skill-creator skill that guides you through the skill creation process.

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Quick Start

1

Load the skill-creator

/use skill-creator
2

Describe your skill

Tell Codex what you want the skill to do and provide examples:“I want to create a skill for rotating and editing PDF files. Users should be able to say things like ‘rotate this PDF 90 degrees’ or ‘extract text from this PDF’.”
3

Let Codex create it

Codex will:
  • Plan the reusable skill contents (scripts, references, assets)
  • Initialize the skill directory with proper structure
  • Generate SKILL.md with frontmatter and instructions
  • Create any necessary helper scripts
4

Validate and iterate

# Codex will run validation automatically
scripts/quick_validate.py path/to/skill-folder

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Skill Creation Process

The skill-creator follows this workflow:
  1. Understand the skill - Gather concrete examples of how the skill will be used
  2. Plan reusable contents - Identify scripts, references, and assets needed
  3. Initialize the skill - Run init_skill.py to create the structure
  4. Edit the skill - Implement resources and write SKILL.md
  5. Validate the skill - Run quick_validate.py to check for issues
  6. Iterate - Test on real tasks and improve based on feedback

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Skill Design Principles

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Concise is Key

The context window is a public good. Skills share it with everything else Codex needs: system prompt, conversation history, other skills’ metadata, and the actual user request.
Default assumption: Codex is already very smart. Only add context Codex doesn’t already have. Challenge each piece of information: “Does Codex really need this explanation?”
Prefer concise examples over verbose explanations.

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Progressive Disclosure

Keep SKILL.md under 500 lines. When approaching this limit, split content into separate files: 
# PDF Processing

## Quick start

Extract text with pdfplumber:
[code example]

## Advanced features

- **Form filling**: See [FORMS.md](FORMS.md) for complete guide
- **API reference**: See [REFERENCE.md](REFERENCE.md) for all methods

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Set Appropriate Degrees of Freedom

Match the level of specificity to the task’s fragility:
  • High freedom (text instructions): Multiple approaches are valid, decisions depend on context
  • Medium freedom (pseudocode/parameterized scripts): Preferred pattern exists, some variation acceptable
  • Low freedom (specific scripts): Operations are fragile, consistency is critical

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Using Skills

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Automatic Triggering

Codex automatically loads skills based on the context of your request. The skill’s description in the frontmatter determines when it triggers.

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Manual Loading

You can explicitly load a skill using the /use command: 
/use skill-name
This ensures the skill is loaded for your current task.

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Managing Skills

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Disabling Project Docs

Skills can be disabled using: 
codex --no-project-doc
Or set the environment variable: 
export CODEX_DISABLE_PROJECT_DOC=1

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Skills Location

Skills are installed to:
  • User skills: $CODEX_HOME/skills/ (typically ~/.codex/skills/)
  • System skills: $CODEX_HOME/skills/.system/ (auto-installed)

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Examples

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Example: PDF Editor Skill

A skill for PDF operations: 
---
name: pdf-editor
description: Edit and manipulate PDF files. Use when the user needs to rotate, merge, extract text, or perform other PDF operations.
---
Bundled resources:
  • scripts/rotate_pdf.py - Rotate PDF pages
  • scripts/merge_pdfs.py - Merge multiple PDFs
  • references/pdf_operations.md - Advanced PDF manipulation guide

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Example: BigQuery Skill

A skill for querying a company database: 
---
name: bigquery-analytics
description: Query company BigQuery database for analytics. Use when the user asks questions about user metrics, revenue, or product usage data.
---
Bundled resources:
  • references/schema.md - Database schema documentation
  • references/finance.md - Finance and revenue metrics
  • references/product.md - Product usage metrics

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Best Practices

Each skill should have a clear, single purpose. Don’t create mega-skills that try to do everything.
Always test bundled scripts by running them to ensure they work correctly. Scripts should be deterministic and reliable.
Information should live in either SKILL.md or reference files, not both. Prefer reference files for detailed information.
Don’t create README.md, CHANGELOG.md, or other auxiliary documentation. Skills should only contain information needed for the AI agent to do the job.
Use lowercase letters, digits, and hyphens only. Prefer short, verb-led phrases that describe the action (e.g., rotate-pdf, not pdf-rotation-tool).

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Next Steps

Create Your First Skill

Follow the step-by-step guide to create a custom skill

Browse Available Skills

Explore curated skills in the official skills repository