| name | skill-normalizer |
| description | Convert skills in non-standard formats to the standard Agent Skills `SKILL.md` format. Validates YAML frontmatter (name, description, license, compatibility, metadata, allowed-tools), directory structure (SKILL.md, scripts/, references/, assets/), and best practices. Use when the user asks to normalize, validate, or fix a skill. |
| license | Complete terms in LICENSE.txt |
Your task is to make skills in non-standard formats compatible with the Agent Skills ecosystem by converting them to the standard SKILL.md format. This document provides the specification for the SKILL.md format, including required and optional fields, directory structure, and best practices for writing effective skills.
Documentation Index
Fetch the complete documentation index at: https://agentskills.io/llms.txt
Use this file to discover all available pages before exploring further.
Specification
The complete format specification for Agent Skills.
Directory structure
A skill is a directory containing, at minimum, a SKILL.md file:
skill-name/
├── SKILL.md # Required: metadata + instructions
├── scripts/ # Optional: executable code
├── references/ # Optional: documentation
├── assets/ # Optional: templates, resources
└── ... # Any additional files or directories
SKILL.md format
The SKILL.md file must contain YAML frontmatter followed by Markdown content.
Frontmatter
| Field | Required | Constraints |
|---|
name | Yes | Max 64 characters. Lowercase letters, numbers, and hyphens only. Must not start or end with a hyphen. |
description | Yes | Max 1024 characters. Non-empty. Describes what the skill does and when to use it. |
license | No | License name or reference to a bundled license file. |
compatibility | No | Max 500 characters. Indicates environment requirements (intended product, system packages, network access, etc.). |
metadata | No | Arbitrary key-value mapping for additional metadata. |
allowed-tools | No | Space-separated string of pre-approved tools the skill may use. (Experimental) |
**Minimal example:**
---
name: skill-name
description: A description of what this skill does and when to use it.
---
Example with optional fields:
---
name: pdf-processing
description: Extract PDF text, fill forms, merge files. Use when handling PDFs.
license: Apache-2.0
metadata:
author: example-org
version: "1.0"
---
name field
The required name field:
- Must be 1-64 characters
- May only contain unicode lowercase alphanumeric characters (
a-z) and hyphens (-)
- Must not start or end with a hyphen (
-)
- Must not contain consecutive hyphens (
--)
- Must match the parent directory name
**Valid examples:**
name: pdf-processing
name: data-analysis
name: code-review
Invalid examples:
name: PDF-Processing
name: -pdf
name: pdf--processing
description field
The required description field:
- Must be 1-1024 characters
- Should describe both what the skill does and when to use it
- Should include specific keywords that help agents identify relevant tasks
**Good example:**
description: Extracts text and tables from PDF files, fills PDF forms, and merges multiple PDFs. Use when working with PDF documents or when the user mentions PDFs, forms, or document extraction.
Poor example:
description: Helps with PDFs.
license field
The optional license field:
- Specifies the license applied to the skill
- We recommend keeping it short (either the name of a license or the name of a bundled license file)
**Example:**
license: Proprietary. LICENSE.txt has complete terms
compatibility field
The optional compatibility field:
- Must be 1-500 characters if provided
- Should only be included if your skill has specific environment requirements
- Can indicate intended product, required system packages, network access needs, etc.
**Examples:**
compatibility: Designed for Claude Code (or similar products)
compatibility: Requires git, docker, jq, and access to the internet
compatibility: Requires Python 3.14+ and uv
Most skills do not need the `compatibility` field.
metadata field
The optional metadata field:
- A map from string keys to string values
- Clients can use this to store additional properties not defined by the Agent Skills spec
- We recommend making your key names reasonably unique to avoid accidental conflicts
**Example:**
metadata:
author: example-org
version: "1.0"
allowed-tools field
The optional allowed-tools field:
- A space-separated string of tools that are pre-approved to run
- Experimental. Support for this field may vary between agent implementations
**Example:**
allowed-tools: Bash(git:*) Bash(jq:*) Read
Body content
The Markdown body after the frontmatter contains the skill instructions. There are no format restrictions. Write whatever helps agents perform the task effectively.
Recommended sections:
- Step-by-step instructions
- Examples of inputs and outputs
- Common edge cases
Note that the agent will load this entire file once it's decided to activate a skill. Consider splitting longer SKILL.md content into referenced files.
Optional directories
scripts/
Contains executable code that agents can run. Scripts should:
- Be self-contained or clearly document dependencies
- Include helpful error messages
- Handle edge cases gracefully
Supported languages depend on the agent implementation. Common options include Python, Bash, and JavaScript.
references/
Contains additional documentation that agents can read when needed:
REFERENCE.md - Detailed technical referenceFORMS.md - Form templates or structured data formats- Domain-specific files (
finance.md, legal.md, etc.)
Keep individual reference files focused. Agents load these on demand, so smaller files mean less use of context.
assets/
Contains static resources:
- Templates (document templates, configuration templates)
- Images (diagrams, examples)
- Data files (lookup tables, schemas)
Progressive disclosure
Agents load skills progressively, pulling in more detail only as a task calls for it. Skills should be structured to take advantage of this:
- Metadata (~100 tokens): The
name and description fields are loaded at startup for all skills
- Instructions (< 5000 tokens recommended): The full
SKILL.md body is loaded when the skill is activated
- Resources (as needed): Files (e.g. those in
scripts/, references/, or assets/) are loaded only when required
Keep your main SKILL.md under 500 lines. Move detailed reference material to separate files.
File references
When referencing other files in your skill, use relative paths from the skill root:
See [the reference guide](references/REFERENCE.md) for details.
Run the extraction script:
scripts/extract.py
Keep file references one level deep from SKILL.md. Avoid deeply nested reference chains.
Validation
Use the skills-ref reference library to validate your skills:
skills-ref validate ./my-skill
This checks that your SKILL.md frontmatter is valid and follows all naming conventions.
