This error appears when your IDE cannot find a valid MCP endpoint to start a session.

It usually means config was parsed, but no endpoint passed health checks.

What to check first

• client config key is correct (servers vs mcpServers)
• endpoint URL is reachable from your machine
• transport type matches server implementation
• required headers are present
• team policy is not blocking external endpoints

Config sanity checks

VS Code

Use the config key expected by your extension build. A valid JSON file with the wrong root key is often ignored.

Cursor and other MCP clients

Confirm endpoint object contains:

• server name
• command or URL
• args and env where needed
• auth headers

Endpoint validation workflow

1. Open Playground
2. Probe the same endpoint used in IDE config
3. Confirm MCP detection and tool discovery
4. Copy known-good values back into IDE settings

If Playground works but IDE fails, issue is almost always config key, profile scope, or extension cache.

Advanced checks

• check proxy and VPN rules for blocked domains
• verify enterprise endpoint allowlists
• restart IDE after config edits

Related troubleshooting

• Blocked by team admin
• MCP error connection closed (-32000)
• CLI installation guide