Plugin Development

Claude Code plugins are git-versioned bundles of skills, commands, agents, hooks, and MCP servers installable via .claude/marketplaces/. This skill covers the full authoring lifecycle.

Anatomy

my-plugin/
├── .claude-plugin/
│   └── plugin.json           # manifest (required)
├── CLAUDE.md                  # plugin-level instructions
├── skills/
│   └── {skill-name}/
│       ├── SKILL.md
│       └── references/
├── commands/
│   └── {command-name}.md
├── agents/
│   └── {agent-name}.md
├── hooks/
│   └── {hook-name}.sh
├── mcp-server/               # optional
│   ├── src/index.js
│   └── package.json
└── README.md

plugin.json — the manifest

Minimum required fields:

{
  "$schema": "https://claude.local/schemas/plugin.schema.json",
  "name": "my-plugin",
  "version": "1.0.0",
  "description": "Short description under 200 chars.",
  "author": { "name": "You" },
  "license": "MIT"
}

Recommended additions:

{
  "repository": "https://github.com/you/my-plugin",
  "keywords": ["claude-code", "..."],
  "permissions": { "requires": ["read", "write"], "optional": ["bash", "network"] },
  "capabilities": { "provides": ["..."], "requires": [] },
  "context": {
    "entry": "CONTEXT_SUMMARY.md",
    "title": "My Plugin",
    "summary": "≤400 words",
    "maxTokens": 700
  }
}

Authoring a skill

Follow the skill-creator canonical spec:

1. Frontmatter description is the trigger — be specific and "pushy" (name ≥3 contexts where it should fire).
2. Body ≤ 500 lines (per skill-creator guidance).
3. Deep reference content goes in references/ subdir — Claude loads on demand.
4. MCP delegation table: if your skill has heavy reference data, move it to an MCP tool.

Template in plugin-architect agent.

Authoring a command

Commands live in commands/{name}.md. Frontmatter:

---
description: What the command does, under 200 chars.
---

# /command-name

## Usage
...

## Flags
...

The command body is plain markdown executed as a prompt when the user runs /plugin-name:command-name.

Authoring an agent

---
name: agent-name
description: When to invoke; ≥3 trigger phrases.
model: sonnet
allowed-tools:
  - Read
  - Grep
  - Bash
---

# Agent Name

## Role
...

## Approach
...

## Output format
...

Tool restrictions enforce agent scope — an auditor agent shouldn't be able to Write, a research agent doesn't need Bash.

Validation

Run plugin-validator agent on any new/modified plugin. Checks:

• Manifest JSON schema conformance
• Required fields present
• Version is semver
• All referenced skills/commands/agents/hooks exist
• Skill descriptions non-empty and specific
• Agent allowed-tools are real tool names
• Hook scripts have shebang + are executable

Publishing

Plugins live in git repos. Users install via marketplace:

/plugin marketplace add https://github.com/org/marketplace-repo
/plugin install my-plugin

For personal plugins, skip the marketplace — git clone into ~/.claude/plugins/ directly.

Version management

Semver. Breaking changes = major bump. New capabilities = minor. Bug fixes = patch.

Include CHANGELOG.md with a section per version. plugin.json version must match the top CHANGELOG entry.

MCP delegation

Anti-patterns

• Skills with empty or template-leaked descriptions → don't trigger; dead weight.
• Manifests that reference missing files → plugin fails to load silently.
• Hooks without set -euo pipefail → mask errors.
• Agents with allowed-tools: ["*"] → defeats tool restriction.
• Version number not bumped on a release → users don't pick up updates.

Reference

• manifest-schema.md — full plugin.json schema with examples