Claude Cowork plugins and skills

What a plugin can contain

The manifest declares any combination of four component types, and Anthropic documents them plainly:

• Skills. Reusable instructions that teach Claude a workflow.
• Connectors. MCP servers that give Claude access to an external service.
• Agents. Specialised subagents Claude can delegate to.
• Hooks. Scripts that run at defined points in a session.

Installing a plugin installs all of them together, which is the whole reason the format exists. A workflow is rarely just an instruction: it needs the connector that reaches the accounting system, the subagent that handles the fiddly sub-job, and sometimes a hook that fires when a session starts. Once installed, the skills and agents appear as tabs on the plugin, while connectors and hooks get their own pages, and you can enable or disable each piece.

Plugins run in Cowork and in Claude Code, and are not used in chat. Skills are the part that travels: a skill that arrives through a plugin becomes available in chat as well.

How to install one

1. Open Customize in the sidebar, then Plugins.
2. Select Browse plugins. The default marketplace is Anthropic's official catalogue, and you can add others by URL.
3. Select a plugin and click Install. If it ships a connector that needs authentication, you are prompted to sign in.
4. Open the installed plugin to review its skills, connectors, agents and hooks, and turn individual components off if you do not want them.

Two other routes exist. To install something that is not in a catalogue at all, use the upload option on the Plugins page and select the plugin package. To follow a repository, choose Add marketplace and paste its URL: Cowork takes the standard https://github.com/owner/repo form and the owner/repo shorthand, and public GitLab and Bitbucket repositories work too. Click Update on a marketplace to pull its latest plugins.

On Team and Enterprise plans, administrators can require plugins for everyone. Those install automatically, say so on the plugin, and cannot be removed by the person using them.

The limits, before you package something large

The published defaults are 200 MB uncompressed per plugin package, 5,000 files per package, a 512 MB marketplace repository archive, 500 plugins per marketplace, and 25 marketplaces per person. The in-app skill viewer previews files up to 1 MB and shows larger ones as too large to preview, though Claude can still read them at runtime.

Claude for Small Business: the flagship plugin

The clearest example of what a Cowork plugin is for arrived on 15 September 2026. Claude for Small Business is Anthropic's own plugin, it runs in Cowork, and it ships 43 ready-to-run workflows aimed at the operating rhythm of a company rather than at a codebase. It connects to 37 eligible partner services, including QuickBooks, PayPal, HubSpot, Shopify, Salesforce, Stripe, Xero, Square, Gusto, Canva, DocuSign, Google Workspace, Microsoft 365, Slack and Zapier, and where a connector does not exist it works from spreadsheets and statements. It is available on every paid Claude plan, with Team recommended for businesses with more than one user.

The named workflows give the shape of it:

• SMB onboard. The setup run: connect your tools and pick the first tasks.
• Monday brief. Cash position, last week's sales against the week before, what moved in the pipeline, which invoices are overdue, on one page.
• Speed to lead. Qualifies an inbound enquiry, drafts the reply with real calendar availability, and logs it to the CRM.
• Proposal builder. Turns a voice memo, a photo or an RFP into a branded proposal, priced from your past jobs.
• Social content engine. Drafts posts in your voice with on-brand graphics, cut into every format your channels need.
• Close month. Reconciles the books against the payment processors, flags mismatches down to the transaction, and writes a plain-English profit and loss.

Beyond those six the catalogue continues: Plan payroll, Pay the bills, Restock, Tax prep, Grow pipeline, Call list, Marketing Monday, plus two meta-workflows, one that builds a connector for an unsupported tool through Zapier and one that turns a manual weekly task into a schedulable workflow of your own.

The constraint Anthropic repeats is the important one. The skills draft, propose and stage; you approve before anything sends, posts or pays. Workflows begin in approval mode, and automating one is a decision you make afterwards.

The gap at the end of Proposal builder

Read that workflow list again and notice where every one of them stops. Proposal builder ends with a priced, branded proposal in a folder. Monday brief ends with a page you could show somebody. Close month ends with a profit and loss your accountant needs. None of them ends with the thing reaching a person outside your company, because sending is deliberately the part that waits for you.

Which leaves the oldest bad habit in professional services: attach it to an email. The client downloads a file, opens it from their file system, and you never learn whether it was read. For a proposal, which is a document whose entire job is to be opened and acted on, that is the worst possible last mile.

The Stacktree plugin

Stacktree publishes an HTML page to a private, unguessable URL that opens in any browser with no account for the viewer, with an optional passcode or company email gate, an expiry, a read receipt, and replace-in-place so a link you already sent never goes stale.

It ships as a plugin package in the open at github.com/stevysmith/stacktree-skill, in the standard format: .claude-plugin/plugin.json declares the plugin and .claude-plugin/marketplace.json makes the repository itself a marketplace. Inside are the publish skill, the job-shaped skills for client deliverables, agent run reports, daily briefs and status dashboards, and the Stacktree MCP server. Because Cowork accepts a Git repository as a marketplace, that repository URL can be added on the Plugins page directly. It is not listed in Anthropic's own catalogue, and this page will say so until it is.

For agents that read the open skills index instead, the same skill installs with npx skills@latest add stevysmith/stacktree-skill, and every MCP client can reach the hosted server at https://api.stacktr.ee/mcp over OAuth. The verb list is on the MCP publish tool, and the Claude Code side is on publish HTML from Claude Code.