> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mcp-b.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Runtime layering

> Why MCP-B separates the standard browser surface, server runtime, and transports.

MCP-B keeps the standard browser surface separate from its server runtime and
transport adapters. A native implementation or `@mcp-b/webmcp-polyfill`
supplies the strict `document.modelContext` surface.
`@mcp-b/webmcp-ts-sdk` adds `BrowserMcpServer`, which mirrors core tool
operations while providing MCP-B-only capabilities. `@mcp-b/global`
initializes those layers and connects the selected browser transport.

This separation allows a library to depend only on types, a site to use only
the strict polyfill, or an application to install the complete MCP-B runtime.
Core tool registrations remain visible to native browser tooling, while
cleanup can restore the context that existed before initialization.

`navigator.modelContext` remains only as a deprecated compatibility alias. New
integrations use `document.modelContext`.

See the [`@mcp-b/global` reference](/packages/global/reference).