Codex Skill Builder

Create well-structured skills compatible with Codex and the Agent Skills specification (used by

npx add-skill

When to Use

• User wants to create a new skill
• User needs help with skill structure or frontmatter
• User asks about trigger keywords or descriptions
• User wants to publish skills for

  npx add-skill

Skill Structure

Minimal Skill (Single File)

skill-name/
└── SKILL.md

Full Skill (With References)

skill-name/
├── SKILL.md           # Main skill file (required)
├── references/        # Additional documentation
│   └── api-guide.md
├── scripts/           # Helper scripts
│   └── helper.py
└── assets/            # Templates, examples
    └── template.txt

SKILL.md Template

---
name: my-skill-name
description: Clear description of what this skill does. Include trigger keywords like keyword1, keyword2, keyword3 so the agent knows when to activate this skill.
allowed-tools: Read, Write, Edit, Grep, Glob, Bash
model: sonnet
license: MIT
metadata:
  author: your-name
  version: "1.0"
---

# Skill Title

## Purpose
Brief explanation of what this skill provides.

## When to Use
- Scenario 1 (include keywords)
- Scenario 2 (include keywords)
- Scenario 3 (include keywords)

## Process

### 1. Understand the Request
How to analyze what the user needs.

### 2. Gather Context
What information to collect.

### 3. Provide Solution
Step-by-step approach.

## Examples

### Example 1: Basic Usage
**Request:** "Help me with X"
**Response:** [How skill handles it]

## Best Practices
- Practice 1
- Practice 2

## Common Pitfalls
- Avoid X, do Y instead

Frontmatter Reference

Required Fields

name

nextjs-expert

description

Optional Fields

allowed-tools

Read, Write, Edit, Grep, Glob, Bash

model

haiku

sonnet

opus

license

MIT

Apache-2.0

metadata.author

metadata.version

"1.0"

Writing Effective Descriptions

Good description (includes what, when, keywords):

description: Expert in Next.js App Router, server components, and React Server Components. Use when user mentions Next.js, RSC, App Router, server actions, or React server-side patterns.

Bad description (too vague):

description: Helps with Next.js

Skill Types

1. Framework/API Expert

Purpose: Deep knowledge of specific technology Triggers: Framework name, features, patterns Tools:

Read, Grep, Glob

name: fastapi-expert
description: FastAPI web framework expert covering routing, dependencies, Pydantic models, async endpoints, and OpenAPI generation. Triggers on FastAPI, Python API, Pydantic, async web.

2. Code Generator

Purpose: Create boilerplate or scaffolding Triggers: "generate", "create", "scaffold" Tools:

Write, Read, Grep, Glob

name: component-generator
description: Generate React components with TypeScript, tests, and stories. Triggers on generate component, create component, scaffold component.

3. Code Analyzer

Purpose: Review and analyze code Triggers: "review", "analyze", "audit" Tools:

Read, Grep, Glob

name: security-auditor
description: Security code review for common vulnerabilities including XSS, SQL injection, and OWASP Top 10. Triggers on security review, audit code, find vulnerabilities.

4. Workflow Automator

Purpose: Automate development tasks Triggers: Task-specific keywords Tools:

Read, Write, Edit, Bash

name: release-helper
description: Automate release workflows including changelog generation, version bumping, and git tagging. Triggers on release, changelog, version bump, tag release.

5. Data Processor

Purpose: Transform or analyze data Triggers: Format names, transformation keywords Tools:

Read, Write, Edit, Grep

name: csv-processor
description: Parse, transform, and analyze CSV files. Convert between CSV, JSON, and other formats. Triggers on CSV, parse CSV, convert CSV.

Publishing for npx add-skill

Skills following this format work with

npx add-skill

Repository Structure

your-repo/
├── skills/
│   ├── skill-one/
│   │   └── SKILL.md
│   └── skill-two/
│       └── SKILL.md
└── README.md

Installation Commands

# Users install from your repo
npx add-skill your-username/your-repo

# List available skills
npx add-skill your-username/your-repo --list

# Install specific skill
npx add-skill your-username/your-repo --skill my-skill

# Direct link to skill
npx add-skill https://github.com/user/repo/tree/main/skills/my-skill

Installation Locations

~/.Codex/skills/

.Codex/skills/

Interactive Skill Creation

When helping users create skills, gather:

1. Skill name - lowercase-with-hyphens
2. What it does - 1-2 sentence description
3. When to activate - trigger keywords
4. Tools needed - Read, Write, Edit, Grep, Glob, Bash
5. Scope - personal or project

Then generate the SKILL.md with proper structure.

Validation Checklist

Before publishing:

• Name is lowercase with hyphens only
• Description includes trigger keywords
• Description explains both WHAT and WHEN
• SKILL.md filename is uppercase
• YAML frontmatter is valid (no tabs)
• Only necessary tools are requested
• Examples are included
• Under 500 lines (move details to references/)

Troubleshooting

Skill Not Activating

1. Check description has specific keywords
2. Verify file is named

   SKILL.md

   (uppercase)
3. Confirm path:

   ~/.Codex/skills/name/SKILL.md

   or

   .Codex/skills/name/SKILL.md

4. Validate YAML syntax (no tabs, proper indentation)
5. Restart Codex

Skill Conflicts

Multiple skills with similar triggers:

• Make descriptions more specific
• Use distinct keywords
• Consider combining into one skill

Resources

• Agent Skills Spec: https://agentskills.io
• Codex Docs: https://docs.anthropic.com/en/docs/Codex
• npx add-skill: https://github.com/vercel-labs/add-skill