> ## 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.

# Essential concepts

> Understand where MCP-B fits, how its runtime works, and which trust boundaries it preserves.

These explanations cover the concepts this project owns: MCP-B boundaries, runtime layers,
transports, tool lifecycles, and security decisions. For current browser behavior, use the
[WebMCP resources and status page](/explanation/design/spec-status-and-limitations).

## Platform and package boundaries

<CardGroup cols={2}>
  <Card title="What is WebMCP?" href="/explanation/what-is-webmcp">
    Understand the proposal and where browser-hosted tools fit.
  </Card>

  <Card title="WebMCP and MCP-B extensions" href="/explanation/strict-core-vs-mcp-b-extensions">
    See which capabilities belong to WebMCP and which MCP-B adds.
  </Card>
</CardGroup>

## Architecture

<CardGroup cols={2}>
  <Card title="Runtime layering" href="/explanation/architecture/runtime-layering">
    Follow initialization from the browser API through the MCP-B runtime.
  </Card>

  <Card title="Transports and bridges" href="/explanation/architecture/transports-and-bridges">
    Understand how tools move between pages, frames, tabs, and desktop clients.
  </Card>

  <Card title="Tool lifecycle" href="/explanation/architecture/tool-lifecycle-and-context-replacement">
    Understand registration lifetime, context replacement, and cleanup.
  </Card>
</CardGroup>

## Trust and status

<CardGroup cols={2}>
  <Card title="Security and human control" href="/explanation/design/security-and-human-in-the-loop">
    Understand MCP-B trust boundaries and user-controlled execution.
  </Card>

  <Card title="WebMCP resources and status" href="/explanation/design/spec-status-and-limitations">
    Find upstream specifications, browser support, debugging tools, examples, and tests.
  </Card>
</CardGroup>

For executable guidance, open the [tutorials](/tutorials/index) or [how-to guides](/how-to/index).
For package APIs, open the [package index](/packages/index).