# Copilot Plugin Authoring

> Create, migrate, audit, and validate flat GitHub Copilot plugins and marketplaces with direct agents, skills, hooks, extensions, MCP configuration, canonical source ownership, and isolated runtime tests. Use when adding a plugin, repairing a manifest, packaging existing primitives, or refreshing marketplace governance.

- Skill: `paulasilvatech/copilot-plugin-authoring-3` (Agent Skill)
- Install (CLI): `npx skillmds@latest add paulasilvatech/copilot-plugin-authoring-3`
- Raw SKILL.md: https://api.skillmd.com/api/skills/paulasilvatech/copilot-plugin-authoring-3/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: paulasilvatech (https://skillmd.com/u/paulasilvatech)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/paulasilvatech/copilot-plugin-authoring-3

---


<!-- Generated from harness/github-copilot/plugins/copilot-plugin-development/skills/copilot-plugin-authoring/SKILL.md by harness/claude-code/scripts/convert_from_copilot.py. Edit the source, not this file. -->

# GitHub Copilot plugin authoring

Build self-contained, installable plugin packages from canonical primitives and prove both static contracts and runtime discovery.

## When to invoke

- "Create a plugin from these existing agents and skills."
- "Migrate this plugin to Agent Plugins 1.0."
- "Why does this installed plugin not expose its agents?"
- "Audit every plugin in the marketplace."
- "Add hooks, MCP, or a client extension to a plugin."

## Source and layout decisions

Choose component ownership before editing:

| Mode | Canonical source | Runtime package |
| --- | --- | --- |
| `library` | `harness/github-copilot/agents/` and `harness/github-copilot/skills/` | Agents and skills are generated directly under the plugin's `agents/` and `skills/`. |
| `plugin` | The plugin's own `agents/`, `skills/`, `hooks/`, or `extensions/` | Canonical content stays directly in those plugin-root directories. |
| Mixed plugin-owned | Plugin-local components plus selected shared skills | Keep `componentSource: plugin` and `sharedSkills` in `manifests/plugin-sources.json`, then generate those package copies from the shared harness source. |

Canonical ownership and source references live in
`harness/github-copilot/manifests/plugin-sources.json`, not in the distributed `plugin.json`. A
plugin-owned package may declare `sharedSkills` there to avoid maintaining a second canonical copy.
Do not hand-edit generated shared-source copies.

GitHub Copilot plugins use:

- flat root `plugin.json` without the Agent Plugins `$schema`;
- direct `agents/`, `skills/`, `hooks/`, and `extensions/` paths;
- root `mcp.json`, declared through `mcpServers`, with portable transports;
- no `com.github.copilot/` directory.

Instructions and VS Code prompts are repository workspace customizations, not portable core plugin components. Package a safe publisher skill when they must accompany a plugin.

## Procedure

1. Inspect the intended capability, existing canonical primitives, same-domain plugins, marketplace entry, and ownership mode.
2. Verify current first-party GitHub plugin, marketplace, hook, and Agent Plugins documentation when the user asks for current behavior, the CLI version changed, or local evidence conflicts.
3. Start from `docs/templates/plugin.template.json` and optionally `docs/templates/plugin-mcp.template.json`.
4. Use a valid plugin name that matches `harness/github-copilot/plugins/<name>/`.
5. Reference only coherent agents, skills, hooks, MCP servers, or extensions. Reject componentless manifests and arbitrary “bundle everything” packages.
6. Search for same-name or high-similarity canonical primitives before adding plugin-local content. Reuse a shared skill through `sharedSkills` when the plugin needs a self-contained copy.
7. For shared sources, run `python3 harness/github-copilot/scripts/normalize_plugin_manifests.py` and `python3 harness/github-copilot/scripts/sync_plugin_components.py`.
8. Add or update the alphabetized `.github/plugin/marketplace.json` entry with source, exact manifest description, and exact version.
9. Validate schemas, components, ownership, marketplace coverage, generated drift, capability policy, and redundancy classifications.
10. Install the plugin in an isolated `COPILOT_HOME`, list its skills and MCP servers, invoke a representative namespaced agent, and exercise hooks or extensions when their runtime surface is available.
11. Record dated current-platform evidence in `docs/HARNESS-VALIDATION.md` and regenerate `docs/PLUGIN-AUDIT.md`, `docs/PRIMITIVE-CONTENT-AUDIT.md`, `docs/PRIMITIVE-CAPABILITIES.md`, `docs/PRIMITIVE-REDUNDANCY.md`, and `docs/catalog/github-copilot.md`.

## Required checks

```bash
python3 harness/github-copilot/scripts/validate_primitives.py --strict
python3 harness/github-copilot/scripts/normalize_plugin_manifests.py --check
python3 harness/github-copilot/scripts/audit_plugins.py --check
python3 harness/github-copilot/scripts/audit_primitive_content.py --check
python3 harness/github-copilot/scripts/audit_primitive_capabilities.py --check
python3 harness/github-copilot/scripts/audit_primitive_redundancy.py --check
python3 harness/github-copilot/scripts/generate_catalog.py --check
python3 harness/github-copilot/scripts/sync_plugin_components.py --check
python3 harness/github-copilot/scripts/sync_installed_primitives.py --check
```

Also validate every new skill with the `skill-creator` validator, lint changed workflows with `actionlint`, compile or syntax-check bundled scripts, and run available package tests.

## Runtime acceptance

Static validation is not enough. A representative install must prove the applicable surfaces:

| Surface | Evidence |
| --- | --- |
| Plugin | `copilot plugin list` shows the expected version. |
| Marketplace | `copilot plugin marketplace browse <name>` lists the package. |
| Agent | `copilot --agent <plugin>:<agent>` resolves and runs. |
| Skill | `copilot skill list --json` reports `source: plugin`. |
| MCP | `copilot mcp list` shows each configured server. |
| Hook | A safe simulated payload or tool call produces the expected decision. |
| Client extension | Package install, mirror checks, dependency pinning, syntax, tests, and an interactive client test when available. |

Reinstall into a fresh isolated home after package changes because GitHub Copilot CLI caches installed content.

## Safety and quality

- Pin executable dependencies, actions, container images, and MCP packages to reviewed versions or digests.
- Embed no token, secret, tenant value, or private endpoint.
- Keep extension imports tied to an exact upstream commit and preserve source and license metadata.
- Do not claim a client extension works in non-interactive CLI merely because installation succeeds.
- Do not translate Agent Plugins MCP configuration to workspace MCP by copying it verbatim; map transports and validate the result.
- Do not refresh evidence dates without repeating the check.

## Troubleshooting

| Symptom | Likely cause | Resolution |
| --- | --- | --- |
| Skills load but agents do not | Manifest omits or mispoints the direct agent directory | Declare `agents: "agents/"` and verify the files are directly present. |
| Manifest contains repository-only metadata | Canonical ownership leaked into the distributed package | Move it to `manifests/plugin-sources.json` and normalize. |
| MCP server is absent | Legacy `.mcp.json`, missing schema, or wrong transport vocabulary | Use root `mcp.json` and the Agent Plugins MCP schema. |
| Hook does not fire | Wrong direct path or non-executable script | Point `hooks` to the plugin-root config and run direct plus live payload tests. |
| Marketplace install is stale | Version or entry differs from manifest | Synchronize description/version and reinstall in a fresh home. |
| Audit reports drift | Canonical source changed without regeneration | Run the declared normalizer, importer, synchronizer, or catalog generator. |
| Same skill exists in shared and plugin sources | Plugin copied and then edited a shared capability | Keep one shared canonical package, declare it in `sharedSkills`, and regenerate the plugin copy. |

## Limits

- Use the `copilot-primitive-architect` agent when package boundaries or component ownership are ambiguous.
- Use `skill-creator` for any skill created or repaired as part of the package.
- Do not import third-party code without verified provenance, license metadata, exact upstream commit, and applicable tests.

## Output template

```markdown
## Plugin authoring result

**Plugin:** <name>
**Version:** <version>
**Ownership:** <library|plugin>
**Status:** <created|migrated|repaired|blocked>

### Components
- Agents: <count>
- Skills: <count>
- Hooks: <count>
- MCP servers: <count>
- Client extensions: <count>

### Validation
- Schemas: <result>
- Repository gates: <result>
- Isolated install: <result>
- Runtime surfaces: <result>
- Unavailable tests: <reason or none>
```

## Quality gate

- [ ] Package purpose and component composition are coherent.
- [ ] Canonical ownership and generated mirrors are explicit.
- [ ] Manifest, MCP, hook, skill, and marketplace contracts pass.
- [ ] Dependencies and upstream sources are pinned.
- [ ] Isolated install proves every claimed runtime surface or reports an unavailable client test.
- [ ] Audit, catalog, synchronization, and repository gates pass.
- [ ] Current claims have dated first-party or runtime evidence.