Short version. A skill is a folder Claude loads only when a task needs it. A plugin is the Claude Code package that ships skills. You install a plugin with two slash commands, right inside Claude Code:

/plugin marketplace add anthropics/skills
/plugin install document-skills@anthropic-agent-skills

No git clone, no npm, no config file to edit by hand. The first line registers a marketplace; the second installs a pack from it — and the string after the @ is the marketplace's id, not the repo name. That's the whole mechanic. The rest of this piece is which two repos to start with and when to skip them and write your own.

Skill vs plugin vs marketplace — the 30-second model#

The words get used interchangeably and they shouldn't be.

So the capability is the skill, the package is the plugin, the store is the marketplace. Keep those straight and the commands stop looking arbitrary.

Repo 1: anthropics/skills — the reference, and real output#

anthropics/skills is Anthropic's own public Agent Skills repository and the marketplace behind them. Two reasons to install it first.

The document skills turn Claude from something that describes a spreadsheet into something that writes the .xlsx. It ships create-and-edit skills for PDF, DOCX, PPTX, and XLSX — the difference between "here's the report text, paste it into Word yourself" and a file you can open:

/plugin marketplace add anthropics/skills
/plugin install document-skills@anthropic-agent-skills

The example skills are the other reason: working skills (MCP-server generation, web-app testing, branding) you can read to learn the format, plus a spec/ folder with the specification and a template/ you copy to start your own.

/plugin install example-skills@anthropic-agent-skills

One license note before you ship anything customer-facing: most of the repo is Apache-2.0, but the four document skills are source-available, not open source. Read LICENSE before you bundle them into a product.

Repo 2: obra/superpowers — a methodology, not a tool#

obra/superpowers (MIT) is the one making the rounds this week, and it's a different shape. It doesn't add a capability; it installs a discipline. The pack is a full software-development methodology expressed as composable skills — test-driven development, systematic debugging, verification-before-completion, writing and executing plans, subagent-driven development, git-worktree management.

The trick is that these skills are written to fire automatically before the relevant work, not to wait to be asked. Point a coding agent at a change and it runs the TDD loop and the debugging routine by default instead of when you remember to nag it.

/plugin install superpowers@claude-plugins-official

Or add the author's own marketplace first, then install:

/plugin marketplace add obra/superpowers-marketplace
/plugin install superpowers@superpowers-marketplace

When to install a pack, when to write your own#

Here's the decision, because "install everything" is how you drown your context in skills that never fire.

Install a maintained pack when you want a capability now and someone else will keep it current: document generation, a disciplined dev loop, anything general. Write your own one-file skill when the behavior is specific to your repo — your deploy steps, your review checklist, your house voice. A skill is just a folder with a SKILL.md, so authoring one is a five-minute job, and because skills use an open format they port to any skills-compatible agent. If you've never written one, start from the template in anthropics/skills and our walkthrough — the hard part isn't the file, it's the description line that decides whether the skill ever triggers.

Most founders end up doing both: a couple of installed packs for the general muscle, a handful of hand-written skills for the parts only you know. That's the right shape. The wrong shape is a long, permanent system prompt doing the job a skill would do for free the 95% of the time it isn't needed.