add-plugin - SKILL.md Agent Skill

name: add-plugin description: >- Install a Claude Code plugin and register it in plugins.json so the full team can replicate the install. Use this whenever adding a new plugin to the project — it keeps plugins.json in sync with what is actually installed. argument-hint: >- <name@marketplace> [--repo <owner/repo>] user-invocable: true allowed-tools: Read, Edit, Bash

Add Plugin

Role: implementation. This skill installs a Claude Code plugin and adds it to plugins.json so ./install.sh stays the source of truth for the project's plugin set.

You have been invoked with the /add-plugin skill.

Implementation constraints

Always update plugins.json. Installing without registering defeats the purpose — the whole point is reproducibility.
Derive marketplace from the identifier. The name@marketplace format encodes both; never ask the user to repeat information already in the argument.
Do not duplicate entries. Check plugins.json before adding; if the plugin is already registered, report it and stop.
Be concise. Report only the outcome — no narration of each step.

Parse Arguments

Arguments: $ARGUMENTS

Required: plugin identifier ($0) in name@marketplace format — e.g. cab-killer@cab-killer or skill-creator@claude-plugins-official.

Optional:

--repo <owner/repo>: GitHub repository to register as the marketplace source before installing (e.g. bdfinst/cab-killer). Required for plugins not on an official marketplace.

Steps

1. Parse arguments

Extract:

NAME — the part before @ in $0
MARKETPLACE — the part after @ in $0
REPO — value of --repo, or empty string if not provided

2. Check for existing registration

Read plugins.json. If .plugins[] already contains an entry with "name": "<NAME>", report:

<NAME> is already registered in plugins.json. Nothing to do.

and stop.

3. Register marketplace (if --repo provided)

If REPO is non-empty, run:

claude plugin marketplace add <REPO>

If this fails, report the error and stop — do not proceed to install.

4. Install the plugin

Run:

claude plugin install <NAME>@<MARKETPLACE>

If this fails, report the error and stop — do not update plugins.json for a plugin that did not install successfully.

5. Add to plugins.json

Append a new entry to the plugins array in plugins.json:

If REPO is non-empty:

{
  "repo": "<REPO>",
  "marketplace": "<MARKETPLACE>",
  "name": "<NAME>",
  "required": true
}

If REPO is empty (official marketplace):

{
  "marketplace": "<MARKETPLACE>",
  "name": "<NAME>",
  "required": true
}

6. Report

Installed:  <NAME>@<MARKETPLACE>
Repo:       <REPO or "official marketplace">
plugins.json: updated