mcp.shared.exceptions.McpError: Cannot read properties of undefined (reading 'vendor') #168
Description
I tested a simple MCP server example using fastmcp via npm install fastmcp, and when I connect a mcp client, I get this error on the client:
mcp.shared.exceptions.McpError: Cannot read properties of undefined (reading 'vendor')
This happens because npm install fastmcp was not installing some of these required dependencies:
"@modelcontextprotocol/sdk": "^1.17.2",
"@standard-schema/spec": "^1.0.0",
"execa": "^9.6.0",
"file-type": "^21.0.0",
"fuse.js": "^7.1.0",
"mcp-proxy": "^5.5.4",
"strict-event-emitter-types": "^2.0.0",
"undici": "^7.13.0",
"uri-templates": "^0.2.0",
"xsschema": "0.3.5",
"yargs": "^18.0.0",
"zod": "^3.25.76",
"zod-to-json-schema": "^3.24.6"
After adding all these modules, the problem was solved.
I believe your package.json must define this required dependencies or peerDependencies.