> ## 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.

# What is WebMCP?

> Why WebMCP exists, what the browser standard defines, and where MCP-B adds tooling.

WebMCP gives websites a browser-native way to publish structured tools through
`document.modelContext`. The tools run inside the page's origin, authenticated
session, application state, and visible browser context.

That location is the point of the design. Agents get an explicit capability
contract from the site instead of inferring intent from screenshots, DOM shape,
or brittle automation scripts.

The [W3C WebMCP specification](https://webmachinelearning.github.io/webmcp/) is
authoritative for the standard surface. MCP-B supplies implementation and
integration tooling, including the strict polyfill, React bindings, browser
transports, iframe bridges, local relays, and extension tooling. MCP-B
capabilities beyond the standard tool surface are extensions.

For implementation, follow [Build your first tool](/tutorials/first-tool) and
[Choose a runtime](/how-to/choose-runtime).