plugin-builder

Plugin Builder

Create new Cowork plugins from scratch with full skill scaffolding.

Guided workflow: describe capability → generate skill structure → test → package → install.

User input rules

This skill follows the marketplace-wide user-prompt standard in lib/user-prompts.md. Every user prompt MUST use the host client's structured input UI (single-pick, multi-pick, or text-input form). Never freeform plain-text yes/no questions. The only exception is the consent-trigger gate documented in lib/consent.md, which waits for user-initiated phrases like "make the ticket".

Pre-Flight Checks

No pre-flight checks needed. This skill creates local plugin files.

When to Use

Use for:

• Creating brand new plugins with custom skills
• Packaging custom workflows
• Building org-specific capabilities
• Creating skills beyond bootstrap plugins

Do not use for:

• Modifying existing plugins (edit directly)
• Installing plugins from catalog (use /core:install)
• Creating simple one-off scripts (use chat instead)

Workflow

1. Describe the Plugin

Ask user:

• Plugin name (kebab-case, e.g., my-plugin)
• Description (one-line: what does it do?)
• Author/organization
• How many skills? (1-10 recommended)

2. For Each Skill

Ask:

• Skill name (kebab-case, e.g., my-skill)
• Description (when to use it)
• Trigger keywords (what words invoke it?)
• What should it do? (workflow description)

3. Generate Plugin Structure

Create directory in workspace:

/plugins/{plugin-name}/
  .claude-plugin/
    plugin.json
  skills/
    {skill-1}/
      SKILL.md
    {skill-2}/
      SKILL.md
  README.md

Generate:

• plugin.json with metadata
• SKILL.md files with guard rails pattern
• README.md with plugin overview

4. Review & Iterate

Show generated files in chat:

• Ask user to review skill workflows
• Adjust descriptions or triggers
• Refine guard rails if needed

5. Package Plugin

Zip plugin directory:

/plugins/{plugin-name}/ → /plugins/{plugin-name}.plugin

Create .plugin file (zipped archive) in workspace root.

6. Install Plugin

Instructions for user:

• Drag .plugin file into Cowork sidebar
• Restart Claude if needed
• Skills now available as /plugin-name:skill-name

Report:

✓ Plugin created and packaged

Plugin: {plugin-name}
Skills: {skill-1}, {skill-2}, ...

Package: {plugin-name}.plugin
Location: /plugins/

To install:
1. Drag {plugin-name}.plugin into Cowork sidebar
2. Restart Claude
3. Try: /{plugin-name}:help

Guard Rails

• Plugin name is unique
• All skills have descriptions and triggers
• Guard rails pattern applied to all skills
• plugin.json is valid JSON
• Skills reviewed and approved
• .plugin file is created and packaged
• Installation instructions provided

Error Cases

Invalid plugin name: "Use kebab-case (lowercase, hyphens). No spaces or special characters."

Duplicate plugin: "Plugin name already exists. Choose a different name."

Invalid SKILL.md: "Each skill needs name, description, and workflow."

Packaging failed: "Could not create .plugin file. Check file permissions."