These two fields are the only ones required. name must be lowercase with hyphens, max 64 characters, and match the parent directory name. description is what Claude reads at startup to decide when the skill is relevant (max 1024 characters).

Optional Frontmatter Fields

Add any of these to the --- block above to customise behaviour:

Field	Example	Purpose
argument-hint	[issue-number]	Hint shown during autocomplete to indicate expected arguments
disable-model-invocation	true	Prevent Claude from auto-loading. User must type /name explicitly. Use for deploys, sends, destructive ops
user-invocable	false	Hide from the / menu. Claude can still load it automatically. Use for background knowledge
allowed-tools	Read, Grep, Bash(npm *)	Tools Claude can use without asking permission. Space-delimited, supports patterns
model	claude-sonnet-4-6	Override the model when this skill is active. Useful for cost control
context	fork	Run in an [isolated subagent](^A separate Claude instance with its own context. The skill content becomes the subagent's system prompt). Skill content becomes the subagent's prompt
agent	Explore	Which subagent runs when context: fork. Built-in: Explore, Plan, general-purpose, or custom from .claude/agents/
license	Apache-2.0	License name or reference to a bundled LICENSE file
compatibility	Requires git, docker	Environment requirements (max 500 chars)
metadata	key-value pairs	Arbitrary metadata (author, version, etc.)

---

Body Content

Everything below the frontmatter is the instruction body. Claude reads this when the skill is activated. Write whatever helps Claude perform the task. There are no format restrictions.

Good body content includes:

• Step-by-step instructions for the task
• Examples of inputs and expected outputs
• Common edge cases and how to handle them
• References to supporting files in this skill folder

String Substitutions

[Placeholders](^Variables in your SKILL.md that get replaced with real values before Claude sees the content) are replaced with real values before Claude sees the content:

Placeholder	Resolves To
$ARGUMENTS	Everything the user typed after the skill name
$ARGUMENTS[N] or $N	A specific argument by index (0-based)
${CLAUDE_SESSION_ID}	The current session ID
${CLAUDE_SKILL_DIR}	Path to this skill's directory

Example: /my-skill SearchBar React Vue gives $0 = "SearchBar", $1 = "React", $2 = "Vue".

If $ARGUMENTS is not present in the content, arguments are appended as ARGUMENTS: <value>.

Dynamic Context Injection

The ! backtick syntax runs shell commands before the content reaches Claude. Output replaces the placeholder:

• PR diff: !`gh pr diff`
• Dependencies: !`cat package.json | jq .dependencies`
• Changed files: !`git diff --name-only`

This is [preprocessing](^The commands run at skill load time, not during conversation. Claude only sees the final output, not the commands themselves). Claude only sees the final output, not the commands.

---

Supporting Files

Keep SKILL.md under 500 lines. Move detailed material to separate files and reference them from the body:

• references/REFERENCE.md: Detailed documentation loaded on demand
• assets/template.md: Templates and static resources
• scripts/helper.sh: Executable code Claude can run

Use relative paths from SKILL.md. Keep references one level deep. Navigate into these folders to learn more about each.