feat: add mcp package

[joshblack]

Pitch: https://github.com/github/primer/issues/5363

Add an experimental @primer/mcp package that could be used in any context where MCPs are supported. This package runs a server that exposes the following tools:

• get_components: used to discover what components are available from Primer
• get_component: used to get the documentation for a specific component
• get_component_examples: used to get the examples for a specific component (specifically storybook examples around usage)
• get_patterns: used to discover pattern guidance that is available from Primer
• get_pattern: used to get the docs for a specific pattern
• get_tokens: used to get a list of design tokens
• get_*_usage: used to get usage guidelines for foundations

Below is a quick demo showing an idea of someone might interact with it in agent mode (or could be used by the Copilot agent directly)

Screen.Recording.2025-06-19.at.2.58.18.PM.mov

In the future, it would be awesome to include support for:

• init: setup a project that uses Primer
• suggest_design_token: suggest what design token to use for a specific usage
• General migration feedback, including tables and tools (like eslint autofixers) to use to help move to new

Finally, it would be great to have a demo showing how this will help an agent get more context in order to use Primer more effectively.

Changelog

New

• Add @primer/mcp package

Changed

Removed

Rollout strategy

• None; if selected, include a brief description as to why

This is an internal package for now

[changeset-bot]

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Latest commit: 9f60fef

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[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	90.2 KB (0%)
packages/react/dist/browser.umd.js	90.38 KB (0%)

[Copilot]

Pull Request Overview

This PR adds the @primer/mcp package - an experimental MCP (Model Context Protocol) server that exposes Primer design system components, patterns, and design tokens to AI tools. The server provides various tools for AI agents to discover and get documentation about Primer components, patterns, and design tokens.

Key changes:

• Added a complete MCP server implementation with tools for components, patterns, and design tokens
• Integrated with existing Primer documentation by fetching and converting HTML content
• Created build and packaging configuration for the new npm workspace

Reviewed Changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/mcp/package.json	Package configuration and dependencies for the MCP server
packages/mcp/src/server.ts	Main server implementation with all MCP tools
packages/mcp/src/primer.ts	Data structures and functions for Primer components and patterns
packages/mcp/src/transports/stdio.ts	Entry point for stdio transport
packages/mcp/tsconfig.json	TypeScript configuration
packages/mcp/tsconfig.build.json	Build-specific TypeScript configuration
packages/mcp/rollup.config.js	Rollup bundling configuration
packages/mcp/README.md	Documentation for the MCP package
package.json	Root workspace configuration update

[Copilot]

The bin field points to ./dist/stdio.js but the rollup config outputs the file as ./dist/transports/stdio.js based on the input path. This mismatch will prevent the binary from being found.

Suggested change

	"bin": "./dist/stdio.js",
	"bin": "./dist/transports/stdio.js",

[kendallgassner]

@joshblack I am currently working on tracking how copilot Padawan does at fixing axe scanning violations and have noticed that is awful at fixing violations that use Primer components.

I would love to setup some time to talk through this idea with you. Maybe we can test how this works with resolving axe scanning issues.

[joshblack]

@kendallgassner sounds great to me! Would love to chat about it 😄