Claude Code Plugin

Guide for creating, validating, and managing plugin.json files for Claude Code plugins. Includes schema validation, best practices, and automated tools.

When to Use This Skill

Activate this skill when:

• Creating or editing .claude-plugin/plugin.json files
• Validating plugin.json schema compliance
• Setting up new plugin directories
• Troubleshooting plugin configuration issues
• Understanding plugin manifest structure

Plugin Manifest Schema

File Location

All plugin manifests must be located at .claude-plugin/plugin.json within the plugin directory.

Complete Schema

{
  "name": "plugin-name",
  "version": "1.2.0",
  "description": "Brief plugin description",
  "author": {
    "name": "Author Name",
    "email": "author@example.com",
    "url": "https://github.com/author"
  },
  "homepage": "https://docs.example.com/plugin",
  "repository": "https://github.com/author/plugin",
  "license": "MIT",
  "keywords": ["keyword1", "keyword2"],
  "commands": ["./custom/commands/special.md"],
  "agents": "./custom/agents/",
  "hooks": "./config/hooks.json",
  "mcpServers": "./mcp-config.json",
  "skills": ["./skills/skill-one", "./skills/skill-two"]
}

Required Fields

• name: Plugin identifier (kebab-case, lowercase alphanumeric and hyphens only)

Optional Fields

Metadata:

• version: Semantic version number (recommended)
• description: Brief explanation of plugin functionality
• license: SPDX license identifier (e.g., MIT, Apache-2.0)
• keywords: Array of searchability and categorization tags
• homepage: Documentation or project URL
• repository: Source control URL

Author Information:

• author.name: Creator name
• author.email: Contact email
• author.url: Personal or organization website

Component Paths:

• skills: Array of skill directory paths (relative to plugin root)
• commands: String path or array of command file/directory paths
• agents: String path or array of agent file paths
• hooks: String path to hooks.json or hooks configuration object
• mcpServers: String path to MCP config or configuration object

Field Validation Rules

name

• Format: kebab-case (lowercase alphanumeric and hyphens only)
• Pattern: ^[a-z0-9]+(-[a-z0-9]+)*$
• Examples:
  • Valid: my-plugin, core-skills, elixir-tools
  • Invalid: myPlugin, my_plugin, My-Plugin, plugin-

version

• Format: Semantic versioning
• Pattern: ^[0-9]+\.[0-9]+\.[0-9]+(-[a-zA-Z0-9.-]+)?(\+[a-zA-Z0-9.-]+)?$
• Examples:
  • Valid: 1.0.0, 2.1.3, 1.0.0-beta.1, 1.0.0+build.123
  • Invalid: 1.0, v1.0.0, 1.0.0.0

license

• Format: SPDX license identifier
• Common values: MIT, Apache-2.0, GPL-3.0, BSD-3-Clause, ISC
• Reference: https://spdx.org/licenses/

keywords

• Format: Array of strings
• Purpose: Discoverability, searchability, categorization
• Recommendations: Use lowercase, be specific, include domain terms

Paths (skills, commands, agents, hooks, mcpServers)

• Format: Relative paths from plugin root
• Recommendations: Use ./ prefix for clarity
• Skills: Array of directory paths containing SKILL.md files
• Commands: Can be string (single path) or array of paths
• Agents: Can be string (directory) or array of file paths

Invalid Fields in plugin.json

The following fields are only valid in marketplace.json entries and must NOT appear in plugin.json:

• dependencies: Dependencies belong in marketplace entries, not plugin manifests
• category: Categorization is marketplace-level metadata
• strict: Controls marketplace behavior, not plugin definition
• source: Plugin location is defined in marketplace, not in plugin itself
• tags: Use keywords instead

Validation Workflow

1. Schema Validation

Use the provided Nushell script to validate plugin.json:

nu ${CLAUDE_PLUGIN_ROOT}/scripts/validate-plugin.nu .claude-plugin/plugin.json

This validates:

• JSON syntax
• Required field presence (name)
• Kebab-case naming
• Field type correctness
• Path accessibility (for relative paths)
• Invalid field detection

2. Path Validation

Validate that referenced paths exist:

nu ${CLAUDE_PLUGIN_ROOT}/scripts/validate-plugin-paths.nu .claude-plugin/plugin.json

Checks:

• Skills directories exist and contain SKILL.md
• Command files/directories exist
• Agent files/directories exist
• Hooks configuration exists
• MCP server configuration exists

3. Initialization Helper

Generate a template plugin.json:

nu ${CLAUDE_PLUGIN_ROOT}/scripts/init-plugin.nu

Creates .claude-plugin/plugin.json with proper structure.

Best Practices

Naming Conventions

• Plugin name: Use descriptive kebab-case (e.g., elixir-phoenix, rust-tools, core-skills)
• Avoid generic names: Be specific about the plugin's purpose
• Match directory name: Plugin name should match its directory name

Versioning Strategy

• Use semantic versioning (MAJOR.MINOR.PATCH)
• Increment MAJOR for breaking changes
• Increment MINOR for new features (backward compatible)
• Increment PATCH for bug fixes
• Use pre-release tags for beta versions (1.0.0-beta.1)

Path Organization

Recommended structure:

plugin-name/
├── .claude-plugin/
│   └── plugin.json
├── skills/
│   ├── skill-one/
│   └── skill-two/
├── commands/
└── agents/

In plugin.json:

{
  "skills": [
    "./skills/skill-one",
    "./skills/skill-two"
  ],
  "commands": ["./commands"],
  "agents": ["./agents"]
}

Metadata Completeness

Always include:

• version: Track plugin evolution
• description: Help users understand purpose
• license: Clarify usage terms
• keywords: Improve discoverability
• repository: Enable contributions

Author Information

Include contact information for:

• Bug reports
• Feature requests
• Contributions
• Questions

Common Validation Errors

Error: Invalid kebab-case name

// ❌ Invalid
"name": "myPlugin"
"name": "my_plugin"
"name": "My-Plugin"

// ✅ Valid
"name": "my-plugin"
"name": "core-skills"

Error: Invalid field for plugin.json

// ❌ Invalid (dependencies only in marketplace.json)
{
  "name": "my-plugin",
  "dependencies": ["other-plugin"]
}

// ✅ Valid
{
  "name": "my-plugin",
  "keywords": ["tool", "utility"]
}

Error: Skill path doesn't exist

// ❌ Invalid (path not found)
"skills": ["./skills/nonexistent"]

// ✅ Valid (path exists with SKILL.md)
"skills": ["./skills/my-skill"]

Error: Invalid version format

// ❌ Invalid
"version": "1.0"
"version": "v1.0.0"

// ✅ Valid
"version": "1.0.0"
"version": "2.1.3-beta.1"

Creating a New Plugin

Step 1: Initialize Directory Structure

mkdir -p my-plugin/.claude-plugin
mkdir -p my-plugin/skills

Step 2: Create plugin.json

Use the initialization script:

cd my-plugin
nu ${CLAUDE_PLUGIN_ROOT}/scripts/init-plugin.nu

Or create manually:

{
  "name": "my-plugin",
  "version": "0.1.0",
  "description": "My plugin description",
  "author": {
    "name": "Your Name"
  },
  "license": "MIT",
  "keywords": ["keyword1", "keyword2"],
  "skills": []
}

Step 3: Add Skills

1. Create skill directory: mkdir -p skills/my-skill
2. Create SKILL.md in skill directory
3. Add to plugin.json:

{
  "skills": ["./skills/my-skill"]
}

Step 4: Validate

nu ${CLAUDE_PLUGIN_ROOT}/scripts/validate-plugin.nu .claude-plugin/plugin.json

Step 5: Test

Install locally to test:

claude-code install ./

Hooks Configuration

Hooks can be inline or referenced:

Inline:

{
  "hooks": {
    "onInstall": "./scripts/install.sh",
    "onUninstall": "./scripts/uninstall.sh"
  }
}

Referenced:

{
  "hooks": "./config/hooks.json"
}

MCP Servers Configuration

MCP servers can be inline or referenced:

Inline:

{
  "mcpServers": {
    "filesystem": {
      "command": "mcp-server-filesystem",
      "args": ["./workspace"]
    }
  }
}

Referenced:

{
  "mcpServers": "./mcp-config.json"
}

Troubleshooting

Plugin Not Loading

• Verify plugin.json exists at .claude-plugin/plugin.json
• Check JSON syntax is valid
• Ensure name field is present and kebab-case
• Validate all path references exist

Skills Not Found

• Check skill paths in plugin.json match actual directories
• Ensure each skill directory contains SKILL.md file
• Verify paths use relative format (./skills/name)

Commands Not Appearing

• Verify command paths exist
• Check commands are .md files or directories containing .md files
• Ensure paths are relative to plugin root

Validation Fails

Run validation with verbose output:

nu ${CLAUDE_PLUGIN_ROOT}/scripts/validate-plugin.nu .claude-plugin/plugin.json --verbose

References

For detailed schema specifications and examples, see:

• references/plugin-schema.md: Complete JSON schema specification
• references/plugin-examples.md: Real-world plugin.json examples

Script Usage

All validation and utility scripts are located in scripts/:

• validate-plugin.nu: Complete plugin.json validation
• validate-plugin-paths.nu: Verify all referenced paths exist
• init-plugin.nu: Generate plugin.json template
• format-plugin.nu: Format and sort plugin.json

Execute scripts with:

nu ${CLAUDE_PLUGIN_ROOT}/scripts/[script-name].nu [args]