tomevault-io 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)
- Metadata (name + description) - always in context (~100 tokens per skill)
- SKILL.md body - loaded when skill triggers (keep under 5k words)
- 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, testingreferences/skill_examples.md- Concrete skill examples with new features
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