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@mcp-b/transports provides the transport classes that move MCP messages through browser boundaries such as tabs, iframes, extensions, and user scripts. It is the package you use when you need to choose or control the message path directly.

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When to use this package

  • You are connecting an MCP server or client across postMessage, iframe, or extension boundaries.
  • You need direct access to transport options such as allowed origins or connection IDs.
  • You are building on top of the lower-level browser transport primitives.

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When not to use this package

  • You want the runtime wired up automatically. Use @mcp-b/global.
  • You want the high-level iframe custom element instead of raw iframe transports. Use @mcp-b/mcp-iframe.

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Where it sits in the package graph

The transport classes sit beside the SDK layer and under several higher-level packages. @mcp-b/global, @mcp-b/react-webmcp, and @mcp-b/mcp-iframe all depend on transport behavior.

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First step

Choose the transport pair that matches your boundary, then connect it to a server or client. The reference page lists every class, option surface, and security boundary.

Reference

Transport classes, option tables, and connection examples.

Bridge tools across iframes

Practical iframe transport setup.

Transports and bridges

Conceptual background on how tools move between boundaries.

mcp-iframe overview

The higher-level wrapper built on the iframe transports.