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2026-09-22 • 5 min read • Fix

How to Fix an MCP Server That Isn't Connecting

How to separate a URL that is not answering from a client that was not restarted, using the hosted MCP Studio endpoint and a curl check.

"It won't connect" covers two different failures, and they ask for opposite fixes. Either the hosted URL is not answering, or the client is still holding yesterday's config. Changing both at once is how an afternoon disappears.

Prove the server first, from a machine that is not your editor.

What connecting means

The client can call the hosted endpoint and receive a tool list. That endpoint looks like this:

https://appatools.com/mcp-studio/api/mcp/your-server-name

The wizard page and the dashboard will not accept an MCP call. If that is the URL saved in Claude or Cursor, the server was never the problem. MCP Studio hosts the real URL. You copy it from the server's setup page. On the dashboard, the status should be active.

Why curl comes before the client

A tool list from curl means the server is up. The remaining work is the client: the URL, the header, and a restart.

A 401 means the token. It is missing, revoked, or issued for a different server. Tokens are one server each. "That access token is not valid for this MCP server" is a real token pasted from the wrong Access panel.

An empty answer after a tool list is not a connection failure. Indexing can still be running. That is returning the wrong information, after you have tools listed.

Check the server in MCP Studio

MCP Studio is the no-code builder on Appa Tools. Open the server you already deployed. You do not rewrite it to test the connection.

  1. Copy the URL from the setup page. It contains /api/mcp/ and the server name.
  2. Confirm the server is active on the dashboard.
  3. For a private server, copy a current token from Access. It starts with mcps_live_. A lost token cannot be displayed. Revoke it and create a new one. The header format is in the private servers guide.
  4. Run curl, then restart the client. Cursor, Claude Desktop, and Windsurf read MCP config at startup.

For a public server:

curl -X POST https://appatools.com/mcp-studio/api/mcp/your-server \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

For a private server:

curl -X POST https://appatools.com/mcp-studio/api/mcp/your-server \
  -H "Authorization: Bearer mcps_live_your_token_here" \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

Claude on the web calls a URL on the internet. A server that exists only on your laptop will not connect that way. Use the hosted URL. If you do not have a server yet, create one in the wizard.

Check that it works

A tool list in the curl response means the server is answering. Update the client to that exact URL and restart it. The client should show the same tools.

Curl works and the client does not. The client is not sending the header, or it was not restarted. Claude's version is not showing up in Claude. Cursor's is not showing up in Cursor.

It connected yesterday. Check whether the token was revoked or the server was switched to private after the client was configured with only a URL.

If it is still not connecting

Change one thing. Replace the URL, or replace the token, then run curl again. Do not edit the client until curl lists tools. The longer order, once the connection is up, is Debug an MCP server.

Fix the connection today

Open your server in MCP Studio and copy the URL from the setup page. Run the public or private curl command above. When it lists tools, paste that same URL into the client and restart.

Where to go next