> ## 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.

# Transports and bridges

> Why WebMCP needs transports when page-hosted tools cross browser boundaries.

WebMCP tools execute inside a page, while a consumer may run in an iframe,
browser extension, userscript, or desktop MCP client. A transport carries tool
discovery, calls, results, and lifecycle notifications across that boundary
without changing where the tool runs.

`@mcp-b/transports` implements low-level tab, iframe, extension, and userscript
paths. `@mcp-b/mcp-iframe` wraps iframe forwarding.
`@mcp-b/webmcp-local-relay` connects browser tools to desktop clients through
localhost and stdio. Upstream `chrome-devtools-mcp` uses the Chrome DevTools
Protocol for coding-agent workflows.

Each bridge establishes a security boundary. Origin validation, connection
identity, extension permissions, and relay exposure must be configured in the
corresponding package. Tool execution remains in the page.

Start with the [`@mcp-b/transports` reference](/packages/transports/reference).