MCP server c2n Web Components

@c2n/mcp

Model Context Protocol server that exposes the c2n web components to AI agents: component APIs (attributes, slots, events, native CSS parts, CSS variables with their theme tokens), usage and gallery examples, curated presets, the @c2n/theme tokens, variant code generation and the application workflow guides. Everything is bundled in data/registry.json, so it works offline in any project.

Use

The server uses stdio and can be launched by any MCP host:

npx -y @c2n/mcp

Claude Code project .mcp.json:

{ "mcpServers": { "c2n": { "type": "stdio", "command": "npx", "args": ["-y", "@c2n/mcp"] } } }

Codex project .codex/config.toml:

[mcp_servers.c2n]
command = "npx"
args = ["-y", "@c2n/mcp"]

Google Antigravity project .agents/mcp_config.json uses the same mcpServers command/args structure as the Claude example. The @c2n/skill package can install the skill and merge these configurations automatically.

Run the server from a project directory: it reports which @c2n/* packages are installed and serves the bundled API when the installed version differs. The registry is packaged locally, so tool calls do not require network access after installation.

Use c2n-mcp --version to inspect the installed server version and c2n-mcp --help for CLI usage.

The MCP server supplies structured component facts; it does not install component packages or edit an application by itself. Pair it with @c2n/skill when you also want the agent to follow c2n's application, theming and variant conventions. See the AI tools guide for the complete setup and example prompts.

Verify the connection

Restart the agent after adding its MCP configuration, then ask it to use the c2n MCP server to list components or inspect c2-button. A connected client should expose the tools below and report @c2n/* packages installed in the current project. If the server cannot start, run npx -y @c2n/mcp --version in that project to distinguish an npm/runtime problem from an MCP client configuration problem.

Tools

Tool	Purpose
list_components	Every component with tag, package, category, description, installed version
search_components	Free-text search across names, descriptions, attributes, slots, events, examples, icons
get_component	Full API of one component, CSS variables grouped by part/state with their theme token
get_examples	Usage rows and gallery cards; view: "index" lists every look (summary, screenshot)
search_examples	Find a look across every component's gallery ("glass", "pill", "underline")
get_presets	Curated presets as CSS variable values
get_theme	The --c2-theme--* tokens, install/mapping snippets; per-component mapping with tag
generate_variant	CSS class / HTML + style / Lit subclass / JSON from overrides, a preset or a gallery card
validate_markup	Checks markup/CSS you wrote: native controls to replace, unknown tags/attributes/slots/events/variables
get_workflow_guide	workflow, theming, variant-components, frameworks

Gallery cards are served with a generated summary of what they change and CSS whose colours follow the --c2-theme--* tokens wherever a literal equals a token's value (var(--c2-theme--color-outline, #d4d4d8)), so a copied card follows the application's theme and dark mode. Each card also links light and dark PNG captures hosted with the docs site (gallery-shots/<component>/<slug>.<theme>.png, written by apps/ui/scripts/gallery-shots.mjs in the Pages deploy).

Validate from the command line

validate_markup is also a CLI, for CI and editor hooks. It reads HTML, JSX/TSX, Vue, Svelte, Astro, Angular and Lit templates and CSS, and checks them against the API of the @c2n/* packages the project has installed:

npx -y @c2n/mcp validate src            # exit 1 on errors
npx -y @c2n/mcp validate src --strict   # warnings fail too (native controls, box styling on a c2 host)
npx -y @c2n/mcp validate --hook         # Claude Code PostToolUse hook: reads the payload on stdin

It reports native <button>/<input>/<select>/<textarea>/<dialog>/<details>/<progress> elements that a c2-* element replaces, unknown c2-* tags, attributes, slots and --c2-* variables (with "did you mean"), events a c2-* element does not fire (with its event list), a static camelCase attribute the element ignores (rowKey for row-key), and box styling on a c2-* host (border, padding, background, box-shadow, outline; a radius alone is fine). A line holding c2n-ignore, or the line after a comment holding it, is skipped. In hook mode the findings go to stderr with exit code 2, which Claude Code hands back to the agent; npx -y @c2n/skill install registers that hook in .claude/settings.json.

Resources: c2n://components, c2n://components/{tag}, c2n://theme, c2n://guide/{topic}.

Development

• data/registry.json is an ignored build artifact. npm run build:tools (repo root) regenerates it from the component manifests, docs content, presets and theme, then compiles dist/ and refreshes the committed skill fallback.
• dev, inspect, smoke and npm pack automatically build the registry when needed.
• npm run smoke -w packages/tools/mcp spawns the server over stdio and checks every tool.
• npm run inspect -w packages/tools/mcp opens the MCP Inspector against the source entry (node src/cli.ts, Node 24 type stripping).