@mcp-b/webmcp-ts-sdk exposes BrowserMcpServer, a thin WebMCP adapter that composes the official MCP TypeScript SDK v2 server. It does not subclass or fork McpServer.
When to use this package
- You need direct control over the browser server instead of the automatic
@mcp-b/globalsetup. - You need to mirror MCP tools to an existing
document.modelContext. - You need to backfill tools from native Chrome or expose MCP-B prompts and resources.
When not to use this package
- You are building a typical web application. Use
@mcp-b/global. - You only need the strict WebMCP surface. Use
@mcp-b/webmcp-polyfill. - You only need an MCP server. Use the official
@modelcontextprotocol/server.
What changed in v2
Dynamic registration is no longer a reason to maintain a modified MCP server. SDK v2 owns dynamic tool, prompt, and resource registrations, plus MCP protocol and transport behavior. SDK v2 also owns schema conversion and validation. It accepts Standard Schema implementations such as Zod 4.2 or newer and wraps raw JSON Schema withfromJsonSchema. Zod 3 is unsupported.
BrowserMcpServer retains only the WebMCP boundary:
BrowserMcpServer.connect(customTransport) remains on SDK v2’s legacy 2025-era route. Installing
v2 does not make tab, iframe, or other custom transports speak MCP 2026-07-28. Instance-level
sampling and elicitation requests live on browserServer.mcpServer.server. These SDK APIs are
legacy-only and throw on modern-era v2 instances. See Supporting protocol revision
2026-07-28.WebMCP can register an array-root input schema because arrays are JavaScript objects. MCP requires
tool input schemas to have an object root. The adapter keeps those tools on WebMCP, omits them
from the MCP tool list, and logs a warning.
Where it sits
@mcp-b/global creates the adapter with the current document.modelContext as its native target. The adapter mirrors browser-facing registrations down to that target and delegates MCP work to its composed v2 McpServer.
The reference page describes the adapter methods and its native Chrome behavior. Use the Model Context Tool Inspector recommended by Chrome’s WebMCP documentation to inspect mirrored tools. The MCP TypeScript SDK v2 documentation owns the upstream server API.
Related pages
Reference
BrowserMcpServer APIs, native mirroring, and backfill helpers.
Runtime layering
See how this layer fits between the polyfill and @mcp-b/global.
Strict core and extensions
Separate the standard browser API from MCP-B helpers.
WebMCP standard API
Consult the browser surface and its upstream specification.