tools-only Claude Code Extensions
Claude Code extends the Agent Skills specification with additional frontmatter fields and features. These are optional — skills that use only the base spec remain portable across all compatible tools.
Extended Frontmatter Fields
| Field | Description |
|---|---|
argument-hint |
Hint shown during autocomplete (e.g., [issue-number], [filename] [format]) |
disable-model-invocation |
Set true to prevent Claude from auto-loading; manual /name only |
user-invocable |
Set false to hide from / menu; background knowledge only |
model |
Override the model when this skill is active |
context |
Set to fork to run in an isolated subagent |
agent |
Which subagent type to use with context: fork (e.g., Explore, Plan) |
hooks |
Hooks scoped to the skill's lifecycle |
Invocation Control
By default, both users and Claude can invoke any skill. Two fields restrict this:
# Only the user can invoke (manual trigger for side-effects like deploy)
disable-model-invocation: true
# Only Claude can invoke (background knowledge, not a meaningful user action)
user-invocable: false
| Setting | User can invoke | Claude can invoke |
|---|---|---|
| (default) | Yes | Yes |
disable-model-invocation: true |
Yes | No |
user-invocable: false |
No | Yes |
Subagent Execution
Set context: fork to run a skill in an isolated subagent. The skill content becomes the prompt — the subagent won't have access to conversation history.
---
name: deep-research
description: Research a topic thoroughly
context: fork
agent: Explore
---
Research $ARGUMENTS thoroughly:
1. Find relevant files using Glob and Grep
2. Read and analyze the code
3. Summarize findings with specific file references
Only use context: fork with skills that contain explicit tasks. Skills that provide guidelines without a task ("use these API conventions") return nothing useful from a subagent.
String Substitutions
Skills support dynamic values in content:
| Variable | Description |
|---|---|
$ARGUMENTS |
All arguments passed when invoking the skill |
$ARGUMENTS[N] |
Specific argument by 0-based index |
$N |
Shorthand for $ARGUMENTS[N] (e.g., $0, $1) |
${CLAUDE_SESSION_ID} |
Current session ID |
---
name: fix-issue
description: Fix a GitHub issue
disable-model-invocation: true
---
Fix GitHub issue $ARGUMENTS following our coding standards.
If $ARGUMENTS is not present in the content, arguments are appended as ARGUMENTS: <value>.
Dynamic Context Injection
The !`command` syntax runs shell commands before the skill content reaches Claude. Output replaces the placeholder.
---
name: pr-summary
description: Summarize changes in a pull request
context: fork
agent: Explore
---
## Pull request context
- PR diff: !`gh pr diff`
- PR comments: !`gh pr view --comments`
## Your task
Summarize this pull request.
Commands execute immediately as preprocessing — Claude only sees the output.
Skill Locations
| Level | Path | Scope |
|---|---|---|
| Enterprise | Managed settings | All org users |
| Personal | ~/.claude/skills/<name>/SKILL.md |
All your projects |
| Project | .claude/skills/<name>/SKILL.md |
This project |
| Plugin | <plugin>/skills/<name>/SKILL.md |
Where plugin is enabled |
Higher-priority locations win when names collide (enterprise > personal > project). Plugin skills use plugin-name:skill-name namespacing.
In monorepos, Claude Code auto-discovers skills from nested .claude/skills/ directories relative to the files being edited.