Vercel
WebMCP support is now available experimentally in Vercel’s mcp-handler package. It lets developers expose existing MCP tools to in-browser agents by adding a single script tag to a site.
According to the Vercel changelog, the feature ships in mcp-handler@2.2.0. WebMCP is a proposed web standard for making tools available to agents running inside a browser.
How Vercel WebMCP Support Works
Developers first choose which existing tools should be available in the browser. Those tools are added to the experimental_webMcp configuration object in the MCP handler.
The site then loads a script from its MCP endpoint using the ?webmcp-script parameter. That script registers the selected tools with the page. When an agent calls one, the request is proxied back to the server.
- 1
Upgrade mcp-handler
use version 2.2.0
- 2
Choose the tools
add their names to the experimental_webMcp configuration object
- 3
Load the script
add the MCP endpoint with the ?webmcp-script parameter
- 4
Handle calls
requests return to the MCP server as the signed-in user
The same server-registered tools can therefore be made available to browser agents without rebuilding them as separate browser integrations.
Authenticated Tools Stay on the Server
Calls are proxied to the MCP server as the signed-in user. This means authenticated tools can work without a separate browser-side OAuth flow.
The opt-in configuration also means developers select which tools are exposed. Registering a tool on the MCP server alone does not automatically add it to the page. It must also appear in the experimental_webMcp tools list.
WebMCP remains a proposed standard, and Vercel labels this implementation experimental. The feature is available now through the latest version of mcp-handler.
Frequently asked questions
What is Vercel WebMCP support?
Vercel WebMCP support is experimental functionality in mcp-handler that exposes selected MCP tools to in-browser agents. Developers opt tools in through configuration and load them on a page with a script tag.
How do I add WebMCP support to a site?
Upgrade to mcp-handler@2.2.0, add the required tools to the experimental_webMcp object, then load the script from the MCP endpoint with ?webmcp-script. Calls from the page are proxied back to the MCP server.
Is WebMCP support free?
No pricing or plan requirements were listed. The experimental feature is available in the latest mcp-handler version.
Sources
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