You copy a server block out of another MCP client's setup instructions into your project configuration. It carries a url field and no type field. The session starts, the server does not appear, and the reported problem mentions a missing command. What has happened?

The principle — An entry is classified before it is used, and the classification is driven by the type field rather than by which other fields happen to be present.

Why the key is correct — The documentation states that an entry with a url but no type is a configuration error, because Claude Code reads an entry with no type as a stdio server. Once it has been read that way, the field it looks for next is the command, which is why a URL-only entry complains about a command it never had.

Why the others are wrong — The URL is never used as a connection target, so the endpoint is not involved and cannot be the fault. No executable is missing, because none was ever named. And the entry is read at load time, not validated when the file is saved, which is why saving succeeded and starting did not.

Remember this — When the error names something your entry never contained, suspect that the entry was read as the wrong kind of server.

Sources — Anthropic's Claude Code MCP reference.