feat: add Claude Code plugin for spec-kit commands

[HamedMP]

Summary

• Adds a complete Claude Code plugin that provides spec-driven development workflow commands
• Includes 9 slash commands mirroring the existing template commands
• Adds an SDD (Spec-Driven Development) skill for automatic methodology guidance
• Includes marketplace.json for easy plugin distribution

Plugin Structure

plugin/
├── .claude-plugin/
│   ├── plugin.json          # Plugin manifest
│   └── marketplace.json     # Marketplace catalog
├── commands/
│   ├── constitution.md      # /speckit:constitution
│   ├── specify.md           # /speckit:specify
│   ├── clarify.md           # /speckit:clarify
│   ├── plan.md              # /speckit:plan
│   ├── tasks.md             # /speckit:tasks
│   ├── implement.md         # /speckit:implement
│   ├── analyze.md           # /speckit:analyze
│   ├── checklist.md         # /speckit:checklist
│   └── taskstoissues.md     # /speckit:taskstoissues
└── skills/
    └── spec-driven-development/
        └── SKILL.md          # SDD methodology guidance

Installation

Users can install via:

# Option 1: Direct plugin directory
claude --plugin-dir ./plugin

# Option 2: As marketplace (once merged)
/plugin marketplace add github/spec-kit --path plugin
/plugin install speckit@speckit-plugins

Test plan

• Verify plugin loads with claude --plugin-dir ./plugin
• Test /speckit:specify command creates spec correctly
• Verify skill activates when discussing SDD methodology
• Confirm marketplace.json validates correctly

[adamkwhite]

Hey @HamedMP, thanks for putting this together. I'm a daily Claude Code user so this caught my eye.

Genuine question: what's the practical advantage of wrapping the spec-kit templates as a Claude Code plugin versus just referencing them directly in a project's CLAUDE.md or as slash commands pointing at the existing markdown files?

I can see the discoverability angle (someone installs the plugin and gets all 9 commands ready to go), but I'm wondering if you've found specific workflow benefits in practice. For example, does the SDD skill meaningfully change how Claude Code reasons about the spec workflow compared to just including the methodology in project context?

Curious to hear your experience with it