2026-09-22 • 5 min read • Fix

How to Debug an MCP Server

How to debug in a fixed order: the URL answers, the client lists the same tools, indexing has finished, a known question cites the right page, and an out-of-scope question is refused.

A wrong answer and a server that never connected feel the same from the chat window. They are not the same bug. The order you check them in decides whether you spend the hour editing a heading that was never retrieved.

What you are separating

A connection problem, a client config problem, an index that has not finished, and a content problem. Stop at the first step that fails. Change one thing, then run the order again from the top.

MCP Studio will show you, on every plan, whether a client called the server at all. Success on the free dashboard means the call completed. It does not mean the passage was right.

Why the order matters

Curl before headings. If tools/list fails, the page you are about to rewrite was never retrieved.

The client before the content. Curl working and Cursor silent is a client config bug.

A known question before a new one. You need a fact you can check, or every reply looks plausible.

Run the checks against your MCP Studio server

MCP Studio is the no-code builder on Appa Tools. Open the server on the dashboard. You do not write any code to debug it.

The URL answers. tools/list via curl returns the tools you selected in the wizard. If it does not, stay on Fix an MCP server that isn't connecting until curl is boring. An empty tool list means no tools were selected, or you are calling a different server than the one you edited.
The client shows those same tools. Claude's list and Cursor's JSON are separate pages: not showing up in Claude, not showing up in Cursor.
Indexing has finished. The dashboard source is complete. The endpoint exists earlier. Judging paragraphs before that finishes measures a crawl, not the docs.
A question you can answer yourself. Ask for a header name or a limit. Open the citation.
A question the sources do not cover. The server should say so.

Free dashboard fields are volume, success, response time, requests over time, and a breakdown by tool, source, and client. Question text is Core analytics. The passage is Action. The table is in What the questions people ask your docs can tell you.

Check that it works

You: What is the office wifi password?

Assistant: Nothing in this server's content covers an office wifi password. The closest material is the upload authentication guide, which is a different subject.

A confident paragraph on that question means the client may not have called the server. Look for a tool call.

Write down the date, the question, the cited page, and the one change you made. Turning the note into a sheet you can rerun is Test an MCP server for accuracy.

If the known question still misses

A miss on step 4 is content or tool choice, which is returning the wrong information. A retrieval rule is a real change. If you add one, that is the one change for the next pair of questions. See retrieval rules.

Debug one server today

Open the server in MCP Studio and run the five checks in order. Stop at the first failure. Change that one thing, then ask the question you already know. The citation, or an explicit miss, tells you the next edit.