What are agent skills?
An agent skill is a folder with a SKILL.md file that teaches an AI how to do one kind of task, such as reviewing a contract or building a landing page. Claude Code and Codex both read skills in this format. A skill loads only when the task needs it, so you can keep many without crowding every chat.
Prompt, system prompt, skill and knowledge base
| Piece | What it is | When the AI uses it |
|---|---|---|
| Prompt | What you ask, once. | For that one message. |
| System prompt | A standing instruction: role, rules, tone, format. | On every message in the chat. |
| Skill | Step-by-step instructions for one kind of task, in a folder with a SKILL.md file. | Only when the task matches. |
| Knowledge base | Facts and documents the AI should rely on. | When it needs an answer from them. |
What is inside a skill
A skill is a folder. The only required file is SKILL.md: a short description of what the skill is for and when to use it, followed by the instructions. A folder can also hold templates, examples and scripts the instructions refer to.
How to install one
- Claude Code: copy the skill folder into
~/.claude/skills/. - Codex: copy the skill folder into
~/.codex/skills/and restart Codex. - A tool that does not read skill folders: paste the text of SKILL.md into its custom instructions.
Each skill pack from Prompt Builder Skill House includes an install prompt you can paste into your AI, and it will do these steps for you.
Stay safe
Treat a skill like software. Read its SKILL.md and any scripts before you install it, because a skill can tell an AI to run commands on your computer. Install skills only from sources you trust.
How Prompt Builder Skill House uses skills
- Free: write your idea and the app matches skills to it for you.
- Paid plans: a Claude skill pack and a Codex skill pack, rebuilt every month, each with a list of what was added, updated or retired.
- Using another AI model: ask for a custom pack built for that one model.
Questions
What is an agent skill?
An agent skill is a folder with a SKILL.md file that teaches an AI how to do one kind of task, such as reviewing a contract or building a landing page. The AI reads the skill when the task calls for it.
How is a skill different from a system prompt?
A system prompt is one standing instruction for every chat. A skill is a separate set of instructions for one task that the AI loads only when it needs it, so you can keep many skills without crowding every chat.
Are agent skills safe to install?
Treat a skill like software. Read its SKILL.md and any scripts before you install it, because a skill can tell an AI to run commands on your computer. Install skills only from sources you trust.
Where do I get skills?
Prompt Builder Skill House matches skills to your idea for free, and paid plans include a monthly Claude skill pack and a Codex skill pack, each with an install prompt and a list of what changed.
Related: How to write a system prompt.