Packages

Extension-use is split so you install only what you use. Most extensions need two packages: host inside the extension, and client wherever the controller runs.

Not sure?

The package picker tells you which packages your setup needs, and where each one goes.

Package	Install in	What it does	Size (min+gzip)
@extension-use/host	Your extension	defineHost() (router, grants, policy), the content runtime, the frame bridge, the control panel, manifest helpers, the extension-use CLI and no-build bundles	content runtime ≈ 9.3 KB
@extension-use/client	Your web app, site or script	connect() with the frame, page, remote and memory transports, and typed calls	core ≈ 2.1 KB + frame ≈ 0.8 KB
@extension-use/protocol	Installed for you	Message types, error codes and zod schemas for every built-in action	types only in clients
@extension-use/wxt	Your WXT extension (dev)	Adds the permissions for your groups and externally_connectable to the generated manifest	build time only
@extension-use/relay	Run with npx, or in your server	The relay that scripts and agents call and the browser dials out to	server
@extension-use/mcp	Run by your MCP client	A paired browser's actions as MCP tools for AI agents	server
@extension-use/testing	Your app (dev)	createMockHost() for unit tests, and Playwright fixtures that load your real extension	dev only
create-extension-use	Run once	npm create extension-use: the wxt, plain and vanilla templates	n/a

Which ones do I need?

You want to…	Packages
Drive the extension from a web app in its side panel	host + client
Drive it from your website in a normal tab	host + client
Drive it from scripts, servers or CI	host (with remote on) + relay + client (or plain HTTP)
Let an AI agent use the browser	host (with remote on) + relay + mcp
Build the extension with WXT	add wxt
Test your controller code	add testing
Start from scratch	create-extension-use

All packages share one version and are released together. They are MIT-licensed.