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bmarcurella/copilot-extension-builder

v0.4.0MIT

Interview-driven builder for Copilot agents, skills, and plugins across GitHub Copilot CLI/VS Code, Microsoft 365 Copilot, Copilot Cowork, and Copilot Studio. Helps you decide agent vs plugin vs skill, scaffolds the gaps it owns (GitHub CLI plugin packaging and Cowork), routes to your installed toolkits for the rest, and keeps its own knowledge current from Microsoft Learn and GitHub docs.

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Copilot Extension Builder

An interview-driven builder for Copilot agents, skills, and plugins across every surface you work in as an architect:

  • GitHub Copilot CLI / VS Code — plugins, agents, skills, instructions, prompts, hooks
  • Microsoft 365 Copilot — declarative agents + plugins (MCP server or REST/OpenAPI)
  • Copilot Cowork — skills and plugin packages
  • Copilot Studio — agents and MCP connectors
  • Azure AI Foundry — agents (routed)

Invoke it with /copilot-extension-builder. It first helps you decide what to build (agent vs plugin vs skill, and on which surface), then scaffolds the result — generating real files you can test immediately.

Why this exists

The word plugin means different things on every surface, and most starter content goes stale fast. This builder does three things to fix that:

  1. Decides for you. A short interview routes "agent vs plugin vs skill" and "which host" using a built-in decision framework and capability matrix.
  2. Owns the gaps, routes the rest. It fully scaffolds the things nothing else does (GitHub CLI plugin packaging and Cowork), and routes to the skills you already have installed for Microsoft 365 / Copilot Studio / VS Code primitives — instead of duplicating them and drifting out of date.
  3. Keeps itself current. A self-update step (/sync-knowledge) checks the canonical Microsoft Learn and GitHub docs on a cadence, auto-applies low-risk changes, flags structural ones for review, and records everything in CHANGELOG.md.

What it owns vs routes

You want to build…Behavior
A GitHub CLI plugin (bundle agents/skills/hooks/MCP into plugin.json + marketplace.json)Scaffolds — build-cli-plugin
A Cowork skill or plugin packageScaffolds — build-cowork
A standalone CLI/VS Code agent, skill, instruction, prompt, or hookRoutes → agent-customization
An M365 declarative agent + plugin (MCP or REST)Routes → microsoft-365-agents-toolkit, typespec-create-api-plugin, typespec-api-operations, mcp-create-declarative-agent
A Copilot Studio agent / MCP connectorRoutes → mcp-create-declarative-agent, typespec-create-agent, mcp-copilot-studio-server-generator
An Azure AI Foundry agentRoutes → microsoft-foundry

See references/routing.md for exact hand-offs and references/surface-comparison.md for the full capability matrix.

Install

This folder is the maintainer source of truth — where you author, version, and publish from. Other people never run from this path; they install a published copy.

Make it available to yourself

This folder ships a marketplace catalog, which is the recommended way to install — the Copilot CLI now deprecates direct path/repo installs in favor of plugin@marketplace.

# Register this folder as a local marketplace.
# Use an ABSOLUTE path — a relative ./path is interpreted as a GitHub repo spec.
copilot plugin marketplace add "D:\Personal Agents.Skills.Plugins\copilot-extension-builder"
copilot plugin install copilot-extension-builder@copilot-extension-builder-marketplace
copilot plugin list            # confirm it loaded (4 skills)

Installing the plugin makes its skills available in both Copilot CLI and VS Code. After editing the source, run the install command again to refresh the cache.

Deprecated but handy for quick local iteration: copilot plugin install ./copilot-extension-builder.

Share it with others

Push this folder to a GitHub repo, then have others register the marketplace and install:

copilot plugin marketplace add OWNER/REPO
copilot plugin install copilot-extension-builder@copilot-extension-builder-marketplace

Consumers get future improvements with copilot plugin update copilot-extension-builder.

Direct copilot plugin install OWNER/REPO still works but is deprecated. Before publishing, check author, repository, and homepage in plugin.json. The marketplace entry's source is ".", which assumes this folder is the repository root. If you keep it as a subfolder of a larger repo, change source to that subfolder path (for example "plugins/copilot-extension-builder").

How it stays up to date

Maintainer (you, from this source)Consumer (installed copy)
Where edits goReal files here → you commit & publish${COPILOT_PLUGIN_DATA} only
EffectEveryone benefits via copilot plugin updateLocal notes; prompts you to update

sync-knowledge auto-detects which mode it is in (writable git source = maintainer; read-only install = consumer) and never writes into the read-only install cache. The monitored doc list and cadence live in references/sources.json (check_interval_days defaults to 14).

Layout

copilot-extension-builder/
├── plugin.json                # Agent Plugins 1.0 manifest (metadata only)
├── skills/
│   ├── copilot-extension-builder/   # router + freshness gate (entry point)
│   ├── build-cli-plugin/            # GitHub CLI plugin packaging (+ templates/)
│   ├── build-cowork/                # Cowork skill / package (+ templates/)
│   └── sync-knowledge/              # self-update engine
├── com.github.copilot/
│   └── hooks/hooks.json       # SessionStart staleness reminder (runs ${PLUGIN_ROOT}/scripts/check-freshness.*)
├── references/                # decision framework, capability matrix, routing, links, sources, lessons
├── scripts/                   # check-freshness.ps1 / .sh
├── CHANGELOG.md               # dated record of knowledge-sync changes
└── README.md

License

MIT