MCP Integration in Claude Code
Last reviewed
Correct answer: C. A required environment variable such as an API key was never passed to the server.
Explanation
The principle — Connected and useful are different states, and the gap between them usually means the server started but could not do its job.
Why the key is correct — A server that shows as connected but lists zero tools has started successfully but is not returning a tool list, and the usual reason is that it is missing a required environment variable such as an API key. The fix is to supply the variable in the entry rather than to touch the server itself.
Why the others are wrong — A crash is ruled out by the connected status. Incompatibility would normally show up at connection time and is much rarer than a missing key. And reinstalling changes the package while leaving the environment untouched, so nothing about the symptom would change.
Remember this — Connected with no tools points at what you did not pass in, not at what is installed.
Sources — Anthropic's Claude Code MCP quickstart and configuration debugging guide.
Sources
“If the list is empty, the server started but didn't register any tools, which usually means it's missing a required environment variable such as an API key.”
“A server that shows as connected but lists zero tools has started successfully but isn't returning a tool list.”
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