Plugin Authoring

Plugin Authoring

A Claude Code plugin bundles skills (and optionally commands, agents, hooks, MCP servers) into one versioned, installable unit distributed through a marketplace. Getting the structure and manifests right is what makes it install cleanly and pin to a known version — the failure modes are all in the layout and the JSON.

Structure

my-plugin/
  .claude-plugin/
    plugin.json          # the plugin manifest
  skills/<name>/SKILL.md
  commands/<name>.md     # optional
  agents/<name>.md       # optional
  hooks/                 # optional

The marketplace is a separate repo (or root) with a marketplace.json listing the plugins it offers.

Manifests

plugin.json — identity + version (the thing consumers pin):

{
  "name": "my-plugin",
  "version": "0.2.0",
  "description": "One line on what it provides",
  "author": { "name": "...", "email": "..." }
}

marketplace.json — the catalog entry pointing at the plugin:

{ "name": "my-marketplace",
  "plugins": [{ "name": "my-plugin", "source": "./my-plugin" }] }

The loop that prevents broken releases

1. Build the structure; keep one capability per skill.
2. Validate locally — install the plugin from a local path and confirm the skills/commands actually load before publishing. A manifest that parses but ships a skill that won't load is the classic invisible break.
3. Version deliberately — bump plugin.json version on every change; consumers pin to it, so an unversioned change silently shifts everyone.
4. Publish by updating the marketplace entry, then have a consumer install the pinned version and verify it resolves.

Discipline

• Version-pin in consumers, never float — reproducibility beats "latest."
• One bundled unit, declared per workload — each workload's config names the plugin + version it gets, so what's installed is auditable.
• Don't ship exec scripts inside skills — keep skills as instructions; put any tooling in the plugin's scripts/commands, audited separately.

Adapted from the MIT-licensed softaworks/agent-toolkit plugin-packaging skill (guidance only; upstream's generator script intentionally omitted).