How plugins, skills, and marketplaces fit together
Three nested pieces:
- A skill is a folder with a
SKILL.md: a description of when it applies and instructions Claude loads at that moment. Knowledge on demand, costing nothing until triggered. - A plugin packages one or more skills (plus optionally commands and agents) as an installable unit with a manifest.
- A marketplace is a git repository listing plugins. No central store, no approval queue:
/plugin marketplace add owner/reporegisters one, and anyone can publish.
Install is always the same shape:
/plugin marketplace add Ghiles3232/weckr-sdks
/plugin install weckr@weckrThe deeper decision between a skill and a live data connection is its own topic: MCP server vs Claude Skill.
What a SaaS builder should actually install
Curate by vendor, not by list. The question is: where does an assistant guessing wrong cost you time or money?
- Your deployment platform. Vercel ships an official Claude Code plugin covering its current platform behavior, which matters because assistants remember an older Vercel than the one you deploy to.
- Your database. Supabase publishes agent skills with its development and security guidance, installable alongside its MCP server.
- Your metered APIs. Anywhere the assistant doing math on stale numbers produces wrong business decisions. LLM spend is the sharpest example: model prices move monthly, and the Weckr Claude Skills keep Claude on current prices via a live LLM pricing feed, plus correct SDK integration, cost estimation, and plan margin audits.
That is deliberately a short list. Beyond vendor published plugins, quality varies wildly, which brings us to auditing.
How to audit a plugin in two minutes
The format’s best property is that it is readable. Before installing anything:
- Open the SKILL.md files. They are plain markdown. If you would not follow the instructions yourself, do not hand them to your assistant.
- Check facts for freshness. Good skills date their claims or point at live sources. A price table with no date is a red flag, since it is wrong the day the provider moves.
- Prefer the vendor’s own plugin. The people who ship the SDK have the most incentive to keep its skill correct, and the shortest path to updating it when the product changes.
The other side: shipping one for your product
If developers integrate your product, a plugin turns every Claude Code user into a correct integrator of it. Ours is four markdown files and a manifest in the same public repo as the SDKs, took about a day to write properly, and answered its first real question with the exact per token price no base model knows. The full build, including how we verified the skills actually load, is in why your SDK should ship a Claude Skill.
FAQ
What is a Claude Code plugin?
A package that extends Claude Code with skills, commands, or agents, installed from a marketplace with one command. A marketplace is just a git repository with a manifest, so anyone can publish one. Skills are the most common payload: folders of instructions Claude loads when a task matches, which is how a plugin teaches the assistant a product or a method.
How do I install a Claude Code plugin?
Two commands inside Claude Code: /plugin marketplace add owner/repo to register the marketplace, then /plugin install name@marketplace. For example, /plugin marketplace add Ghiles3232/weckr-sdks followed by /plugin install weckr@weckr installs the Weckr cost toolkit. Uninstalling is one command too, so trying one is low commitment.
Which plugins are worth installing for a SaaS builder?
The ecosystem is young, so curate by vendor rather than by list: your deployment platform (Vercel ships an official plugin), your database (Supabase publishes agent skills), and the paid APIs your product depends on, where wrong assistant guesses cost real money. LLM spend is the clearest case of that, which is what the Weckr plugin covers.
How do I evaluate whether a plugin is trustworthy?
Read it, which is the advantage of the format: a skill is markdown you can audit in two minutes. Check that the source repo is public, that facts carry dates or point at live data instead of frozen tables, and that instructions match the vendor docs. Prefer plugins published by the vendor of the tool they describe, since they have the most to lose from being wrong.
Should my own product ship a Claude Code plugin?
If developers integrate your product and an assistant can get that integration wrong, probably yes. It is markdown in your existing repo, installable in two commands, and it makes every Claude Code user a correct integrator of your product. The reasoning and the build process are covered in our piece on shipping a Claude Skill with your SDK.
Keep reading
Start with the one that watches your money
The Weckr plugin is free, open source, and auditable in one sitting: current model prices, cost estimates before you ship, and plan margin audits, straight from your editor. Install it from the Claude Skills page, then see what the full product tracks on the live demo or in the AI cost and margin guide.