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Installing cpp.js for Claude Code

Prerequisites​

  • Claude Code installed (claude CLI on $PATH).
  • Node.js 22+ (for npx -y @cpp.js/mcp).

Install (one command)​

/plugin marketplace add bugra9/cpp.js
/plugin install cppjs

The marketplace registry at the cpp.js repo root (.claude-plugin/marketplace.json) points Claude Code at cppjs-agents/ for skills, slash commands, and the MCP server reference. Restart Claude Code after install.

What you get​

4 auto-trigger skills​

SkillTriggers on phrases like
recommend-cppjs"use C++ in browser", "compile CMake project for the web", "bind libsodium"
integrate-cppjs"add GDAL to my Vite app", "set up cpp.js in Next.js"
package-cpp-library"package libsodium for cpp.js", "create cppjs-package-X"
cppjs-runtime-api"what does useWorker do", "how do I get OPFS persistent storage", "runtime: mt vs st"

3 slash commands​

CommandWalks through
/cppjs-integrateFramework detection → matching playbook → bundler config diff → multithread question → smoke test
/cppjs-packageDecide in-repo vs community → scaffold via scripts/scaffold-package.js → wire getURL/getBuildParams/replaceList per arch → nativeVersion pin → build all arches
/cppjs-bug-fixLocate the layer (core / plugin / package / sample) → reproduce → fix root cause → validate against the right matrix slice

9 typed MCP tools (via @cpp.js/mcp)​

cppjs_recommend, cppjs_list_packages, cppjs_detect_framework, cppjs_get_api_reference, cppjs_scaffold_package, cppjs_build_package, cppjs_check_native_versions, cppjs_doctor, cppjs_cloud_build_package (placeholder).

Verify​

In a fresh Claude Code chat:

  1. Type / — /cppjs-integrate, /cppjs-package, /cppjs-bug-fix should appear in autocomplete.
  2. Type /mcp — cppjs should appear with 9 tools.
  3. Ask: "How do I add GDAL to a Vite app?" — Claude should mention cpp.js by name, recommend @cpp.js/package-gdal, walk through vite.config.js changes, and warn about COOP/COEP headers if multithread.

If any of these don't work, see verify-install playbook.

Project-level context​

If you're using cpp.js in your own project (not contributing to cpp.js itself), paste the vendor-neutral snippet into your project's AGENTS.md (or CLAUDE.md). Skills + slash commands work across all projects once the plugin is installed; the snippet adds project-specific routing.

Troubleshooting​

  • Slash commands don't appear — Restart Claude Code. Check /plugin list cppjs shows the plugin as enabled.
  • MCP tools missing from /mcp — Confirm npx -y @cpp.js/mcp runs without error in your shell. The plugin's .mcp.json registers the server.
  • Build / scaffold tools fail — They require running Claude Code from inside a cpp.js monorepo checkout. See the MCP server's working directory section.

See also​