Plugins and the marketplace

What a plugin actually is

Technically, a plugin is a Git repo (or a zip archive) that can contain slash commands, skills (domain instructions loaded at the right moment), hooks (scripts triggered on SessionStart, PreToolUse, etc.), preconfigured MCP servers and sub-agents. Claude Code handles updates, enabling and disabling. Since October 1, 2026, it can also ship a mod, code that runs inside Claude Code itself (more on that below, and chapter 20 is all about it).

Before plugins, you had to copy-paste markdown files between projects and explain to each person how to install your workflow. Now one command does it.

Where to find plugins

Skill sync only goes one way, from claude.ai to your machine, and only when you're logged in with your subscription. /skills lists them under claude.ai sync. Handy if you've already built skills in the app. If you don't want them in every project, set "syncClaudeAiSkills": false in your user settings. Plugins you uploaded to claude.ai don't come down on their own: claude plugin marketplace list shows that marketplace ("My Uploads") with the claude plugin marketplace add --claudeai ... command to add it.

You add a marketplace from a GitHub repo, a git URL or a local path. The community directory is open: a plugin being listed there doesn't mean Anthropic audited it.

Install and manage your plugins

From Claude Code, type /plugin. You get the catalog, the descriptions and the install button.

From the terminal, if you already know what you want:

# add a marketplace (once)
claude plugin marketplace add anthropics/claude-plugins-community

# install: name@marketplace
claude plugin install superpowers@claude-plugins-official

# see what's installed, and the configured marketplaces
claude plugin list
claude plugin marketplace list

# a plugin's inventory and projected token cost, before or after install
claude plugin details superpowers

# disable without uninstalling
claude plugin disable superpowers@claude-plugins-official

# update (restart required), uninstall
claude plugin update superpowers@claude-plugins-official
claude plugin uninstall superpowers@claude-plugins-official

# remove auto-installed dependencies you no longer need
claude plugin prune

claude plugins (plural) works too, it's an alias.

Security: read before you install

The routine before every install:

1. Update Claude Code. Security fixes only help if you have them.
2. Read the plugin. claude plugin details <name> for the inventory, then open the repo: hooks/hooks.json and the scripts it calls first, since those run without asking you.
3. Pin a version. In a marketplace, an entry can point to a specific commit (sha). Plugin4Shell showed that isn't enough on its own, but it keeps you from silently receiving an update you haven't read.
4. Install one plugin at a time, and watch what it changes in your session before adding another. Stack five plugins at once and too many skills fire in parallel, you lose track of who does what.

What a plugin costs in context

Every installed skill adds its description to your context, every session. Ten plugins with fifteen skills each add up.

• /skill-doctor lists your skills with their context cost and actual usage (the report opens in the Stats tab of /plugin, v2.1.252 or later). Whatever you haven't used in a month goes.
• claude plugin details <name> gives a plugin's projected cost before you install it. On my machine, claude plugin details superpowers reports 15 skills, one SessionStart hook and about 840 tokens added to every session.
• /usage breaks down the session's consumption by skill, plugin, subagent and MCP server.

The levers are covered in detail in chapter 19.

Four plugins to install first

ralph-loop is off this list. It makes Claude rework the same task in a loop until it's done, and Claude Code now does that on its own with /goal and /loop (chapter 18).

superpowers

About fifteen method skills, in the official marketplace: brainstorming, writing-plans, executing-plans, systematic-debugging, test-driven-development, verification-before-completion, requesting-code-review, subagent-driven-development, using-git-worktrees.

Typical use case: before writing code for a fuzzy feature, the brainstorming skill kicks in (or you ask for it). It pins down intent, requirements and design before the first line, instead of jumping on the first idea.

claude plugin install superpowers@claude-plugins-official

commit-commands

Anthropic's plugin that provides /commit. Lots of people think the command is built in. It isn't. You also get /commit-push-pr (commit, push and open the PR in one go) and /clean_gone (cleans up local branches deleted on the remote).

claude plugin install commit-commands@claude-plugins-official

claude-seo

It comes from the community directory and audits the site in your repo. It checks the technical side (crawlability, Core Web Vitals, security), content (E-E-A-T), JSON-LD schema, images, sitemap and hreflang, plus visibility in AI engines (AI Overviews, ChatGPT, Perplexity). It ships 17 skills and 11 agents, and outputs a health score from 0 to 100.

Use case: you're working on a Next.js site, you run the audit before a deploy, you get the score and a list of priority fixes.

claude plugin install claude-seo@claude-community

claude-blog

Same author as claude-seo, on the writing side: 20 commands and 4 agents that take an article from outline to rewrite, with a score out of 100. It reads MDX, markdown and HTML.

Use case: /blog outline for a structure drawn from Google results, /blog write for the draft with cited sources, then an SEO check before publishing.

claude plugin install claude-blog@claude-community

Mine, if you care about CO2

Outside the ranking, because I wrote it. I code all day with Claude Code and had no idea what it emitted. claude-carbon estimates your session's CO2 and cost locally from your tokens, and shows them in the status line. Every session is stored in a local SQLite database, so the history survives the 30-day transcript purge. It adds /carbon-report (text report), /carbon-card (PNG card) and /carbon-pr (a pull request's footprint).

npx claude-carbon

Or through the marketplace: claude plugin marketplace add gwittebolle/claude-carbon then claude plugin install claude-carbon@claude-carbon. Restart Claude Code afterwards.

Mods: code that runs inside Claude Code

Available since October 1, 2026 (Claude Code v2.1.287 in the terminal), in the CLI and the Code tab of the desktop app. A mod can draw a panel or a banner, pin its own line under the prompt, intercept tool calls and add commands that answer without a Claude turn. Some Claude Code features are mods themselves, like /diff. To write one, describe it in a session or run /plugin-authoring. Before installing someone else's, run claude plugin validate on its folder: it lists what the mod listens to and what it calls. All the details, with two complete, tested mods, are in chapter 20.

Build and publish your plugin

Getting started

claude plugin init my-plugin

The command creates the skeleton in ~/.claude/skills/my-plugin/. It loads on its own in the next session, as my-plugin@skills-dir. You iterate locally before publishing anything. For a mod, init isn't needed: you write its three files directly (chapter 20).

Typical structure

my-plugin/
  .claude-plugin/
    plugin.json          # plugin manifest
  commands/              # slash commands
  skills/                # skills (one folder per skill, with SKILL.md)
  agents/                # sub-agents
  hooks/
    hooks.json           # loaded automatically
  .mcp.json              # MCP servers (optional)
  README.md

Minimal plugin.json

{
  "name": "my-plugin",
  "version": "1.0.0",
  "description": "What the plugin does in one sentence",
  "author": { "name": "your-name" },
  "homepage": "https://github.com/your-handle/my-plugin"
}

Test before publishing

# checks the manifest, skills, agents, commands and a mod's code
claude plugin validate ./my-plugin

# runs the plugin's graded test suite (evals/ folder by default)
claude plugin eval ./my-plugin

claude plugin eval runs test cases (a prompt and grading criteria) against your plugin, and compares them with a session without the plugin. It tells you whether your skill improves the result or not. It runs the plugin on your machine: only use it on plugins you trust.

Publish

1. Push the repo to GitHub (public)
2. If your repo also serves as a marketplace, add a .claude-plugin/marketplace.json that lists your plugins
3. Users add it with claude plugin marketplace add your-handle/my-plugin then install it
4. To show up in the community directory, check the README of the anthropics/claude-plugins-community repo

Full docs: code.claude.com/docs/en/plugins/create.

Sources

• Discover plugins (Claude Code docs)
• Create plugins (Claude Code docs)
• Mods overview (Claude Code docs)
• Claude Marketplace, announcement
• Community directory anthropics/claude-plugins-community