/creating-skills

name: creating-skills
description: Guide for creating Claude Code skills following Anthropic's official best practices. Use when user wants to create a new skill, build a skill, write SKILL.md, update an existing skill, or needs skill creation guidelines. Provides structure, frontmatter fields, naming conventions, and new features like dynamic context injection and subagent execution.

Creating skills

Guide for creating Claude Code skills following Anthropic's official best practices.

Quick start

# 1. Create skill directory
mkdir -p ~/.claude/skills/<skill-name>

# 2. Create SKILL.md with frontmatter
cat > ~/.claude/skills/<skill-name>/SKILL.md << 'EOF'
---
name: <skill-name>
description: <What it does>. Use when <trigger phrases>. <Key capabilities>.
---

# <Skill title>

<Instructions for the skill workflow>
EOF

# 3. Add optional resources as needed
mkdir -p ~/.claude/skills/<skill-name>/{scripts,references,assets}

SKILL.md structure

Frontmatter (YAML between `---` markers)

| Field | Required | Description | |-------|----------|-------------| | `name` | No | Display name. Defaults to directory name. Lowercase, hyphens, max 64 chars. | | `description` | Recommended | What + when + capabilities. Max 1024 chars. Determines when Claude activates the skill. | | `allowed-tools` | No | Tools Claude can use without asking permission when skill is active. | | `argument-hint` | No | Autocomplete hint for arguments. Example: `[issue-number]` | | `disable-model-invocation` | No | `true` to prevent auto-invocation (manual `/name` only). | | `user-invocable` | No | `false` to hide from `/` menu (background knowledge only). | | `model` | No | Model override when skill is active. | | `context` | No | `fork` to run in isolated subagent context. | | `agent` | No | Subagent type when `context: fork`. Built-in: `Explore`, `Plan`, `general-purpose`. | | `hooks` | No | Lifecycle hooks scoped to this skill. |

Invocation control matrix

| Configuration | User can invoke | Claude can invoke | |---------------|-----------------|-------------------| | (defaults) | Yes | Yes | | `disable-model-invocation: true` | Yes | No | | `user-invocable: false` | No | Yes |

Description formula

<What it does>. Use when <trigger phrases>. <Key capabilities>.

Include action verbs ("create", "handle"), user intent ("wants to", "needs to"), and domain keywords users would say.

Directory structure

skill-name/
├── SKILL.md              # Required: instructions (keep under 500 lines)
├── scripts/              # Optional: executable code (deterministic, token-efficient)
├── references/           # Optional: docs loaded into context on demand
└── assets/               # Optional: files used in output, NOT loaded into context
                          #   (templates, images, fonts, boilerplate)

Progressive disclosure (3-level loading)

1. **Metadata** (name + description) - always in context (~100 tokens per skill) 2. **SKILL.md body** - loaded when skill triggers (keep under 5k words) 3. **Bundled resources** - loaded as needed by Claude

Reference supporting files from SKILL.md so Claude knows they exist. Keep references one level deep. For files over 100 lines, include a table of contents.

Scripts vs references vs assets

| Type | Purpose | Loaded into context? | |------|---------|---------------------| | `scripts/` | Deterministic operations, complex processing | No (executed via bash) | | `references/` | Documentation Claude reads while working | Yes, on demand | | `assets/` | Templates, images, fonts for output | No (copied/used in output) |

Only create scripts when they add value: complex multi-step processing, repeated code generation, deterministic reliability. Not for single-command wrappers.

Dynamic features

Context injection

Inject shell command output into skill content before loading:

## Recent commits
!`git log --oneline -5 2>/dev/null`

The output replaces the directive when the skill loads.

String substitutions

Pass arguments to skills invoked via `/skill-name arg1 arg2`:

| Variable | Value | |----------|-------| | `$ARGUMENTS` | Full argument string | | `$ARGUMENTS[0]`, `$ARGUMENTS[1]` | Individual arguments | | `$1`, `$2` | Shorthand for `$ARGUMENTS[N]` |

Subagent execution

Run a skill in isolated context with `context: fork`:

---
name: deep-research
description: Research a topic thoroughly.
context: fork
agent: Explore
---

Degrees of freedom

Match specificity to the task's fragility:

| Level | When to use | Example | |-------|-------------|---------| | **High** (text instructions) | Multiple valid approaches, context-dependent | "Analyze the code and suggest improvements" | | **Medium** (pseudocode/scripts with params) | Preferred pattern exists, some variation OK | Script with configurable parameters | | **Low** (specific scripts, few params) | Fragile operations, consistency critical | Exact sequence of API calls |

Naming conventions

• Lowercase, hyphens between words, max 64 chars
• Styles: gerund (`processing-pdfs`), noun phrase (`github-pr-creation`), prefixed group (`github-pr-*`)

Important rules

• **ALWAYS** write descriptions that include WHAT + WHEN triggers + capabilities
• **ALWAYS** keep SKILL.md under 500 lines, split to references when approaching
• **ALWAYS** reference bundled files from SKILL.md so Claude discovers them
• **NEVER** duplicate info between SKILL.md and reference files
• **NEVER** create wrapper scripts for single commands
• **NEVER** include extraneous files (README.md, CHANGELOG.md, INSTALLATION_GUIDE.md, QUICK_REFERENCE.md)
• **NEVER** explain things Claude already knows (standard libraries, common tools, basic patterns)

References

• `references/official_best_practices.md` - Principles, anti-patterns, quality checklist, testing
• `references/skill_examples.md` - Concrete skill examples with new features