# Cross-Tool Compatibility Reference

Claude Code and GitHub Copilot CLI share the plugin concept but diverge in specific, breaking
ways. **Skills are the portable core. Manifests and agents are where they split.**

Make Claude Code the source of truth — it is the stricter, more fully specified format.
Treat "loads in Copilot CLI" as a tested checklist item per plugin, not an assumption.

---

## Divergence table

| Concern | Claude Code | GitHub Copilot CLI | Portable choice |
|---|---|---|---|
| Marketplace manifest path | `.claude-plugin/marketplace.json` (required) | `.github/plugin/marketplace.json` (primary); also reads `.claude-plugin/` | Put it in `.claude-plugin/` — both read it. Optionally mirror to `.github/plugin/`. |
| Plugin manifest path | `.claude-plugin/plugin.json` (required; only `plugin.json` goes in this dir) | `plugin.json` at **plugin root** | Ship in both locations until verified — see ⚠️ below |
| Skills | `skills/<name>/SKILL.md` | `skills/<name>/SKILL.md` | ✅ Identical |
| Agents | `agents/<name>.md` | `agents/<name>.agent.md` (frontmatter incl. `tools:`) | Diverges — keep portable logic in skills; ship per-tool agent files only when needed |
| Hooks | `hooks/hooks.json` | `hooks.json` at plugin root | Diverges; declare paths in manifest to be safe |
| MCP servers | `.mcp.json` at plugin root | `.mcp.json` at plugin root | ✅ Same |
| Relative `source` | must start with `./` | `./x` and `x` both valid | Always use `./` — valid for both |
| Validate command | `claude plugin validate .` (or `/plugin validate .`) | none documented | Run Claude validator + manual JSON checks for Copilot |
| Install marketplace | `claude plugin marketplace add owner/repo` | `copilot plugin marketplace add owner/repo` | Same shape |
| Install plugin | `claude plugin install <name>@<marketplace-name>` | install by plugin name; `@marketplace` suffix unconfirmed | ⚠️ Verify Copilot install string before documenting |
| Local install (dev) | `claude --plugin-dir ./plugin` | `copilot plugin install ./plugin` | Tool-specific |
| Component paths in plugin.json | Claude defaults to standard dirs; path overrides via marketplace entry only | `"skills": "skills/"`, `"agents": "agents/"`, etc. in plugin.json | Generate per-tool manifests rather than one shared file |

> ⚠️ **UNVERIFIED — test before committing to a layout.**
> Copilot docs confirm it reads the **marketplace** manifest from `.claude-plugin/`. They do NOT
> confirm the same fallback for a plugin's `plugin.json`. Copilot docs show `plugin.json` at plugin
> root; Claude requires it in `.claude-plugin/`. Until verified: ship `plugin.json` in BOTH
> `plugin-name/plugin.json` and `plugin-name/.claude-plugin/plugin.json` (identical content), then
> drop whichever proves redundant.

---

## `@<marketplace-name>` resolution

`claude plugin install startup-cto@my-ai-marketplace` requires the marketplace manifest's
top-level `name` field to be exactly `my-ai-marketplace`. It is **not** the GitHub repo name.
Keep them aligned to avoid confusion, but they are separate fields.

---

## Canonical cross-compatible repo layout

```text
repo-root/
├── .claude-plugin/
│   └── marketplace.json          # both tools read here
├── .github/plugin/
│   └── marketplace.json          # OPTIONAL: Copilot canonical path (mirror)
├── plugins/
│   └── startup-cto/
│       ├── plugin.json           # Copilot root manifest  ┐ ship both until
│       ├── .claude-plugin/       #                        │ the note above is
│       │   └── plugin.json       # Claude manifest        ┘ verified
│       ├── skills/
│       │   ├── fundraising/SKILL.md
│       │   └── hiring/SKILL.md
│       ├── agents/
│       │   ├── startup-cto.md        # Claude
│       │   └── startup-cto.agent.md  # Copilot (only if shipping native agents)
│       ├── hooks/hooks.json          # Claude
│       ├── hooks.json                # Copilot (if hooks used)
│       └── README.md
└── README.md
```

---

## Open questions to resolve before generating layouts

1. **Does Copilot CLI load a plugin whose `plugin.json` lives only in `.claude-plugin/`?**
   Install a test plugin both ways. The answer decides whether to ship one manifest or two.

2. **What is Copilot's exact install-from-marketplace command?**
   Run `copilot plugin install --help`. The `update`/`uninstall` commands take a bare plugin
   name — the `@marketplace` form may not apply.