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Connection Error - Check if your MCP server is running and proxy token is correct #908
Description
Hi,
I'm creating an issue similar to #724 .
I've tried all of the recommendations in issue #724 with the same connection issue. Below is my code for my mcp_server.py.
I'm unable to progress in the tutorial at this point in time.
Any help would be greatly appreciated.
mcp.server.py*
from pydantic import Field # type: ignore
from mcp.server.fastmcp import FastMCP # type: ignore
mcp = FastMCP("DocumentMCP", log_level="ERROR")
docs = {
"deposition.md": "This deposition covers the testimony of Angela Smith, P.E.",
"report.pdf": "The report details the state of a 20m condenser tower.",
"financials.docx": "These financials outline the project's budget and expenditures.",
"outlook.pdf": "This document presents the projected future performance of the system.",
"plan.md": "The plan outlines the steps for the project's implementation.",
"spec.txt": "These specifications define the technical requirements for the equipment.",
}
@mcp.tool(
name="read_doc_contents",
description="Reads the contents of a specified document and returns it as a string.",
)
def read_document(
doc_id: str = Field(description="The ID of the document to read."),
):
if doc_id not in docs:
raise ValueError(f"Document with ID '{doc_id}' not found.")
return docs[doc_id]
@mcp.tool(
name="edit_document",
description="Edits the contents of a specified document with new content.",
)
def edit_document(
doc_id: str = Field(description="The ID of the document to edit."),
old_str: str = Field(description="The string to be replaced in the document."),
new_str: str = Field(description="The new content to write into the document."),
):
if doc_id not in docs:
raise ValueError(f"Document with ID '{doc_id}' not found.")
docs[doc_id] = docs[doc_id].replace(old_str, new_str)
return f"Document '{doc_id}' has been updated."
TODO: Write a resource to return all doc id's
TODO: Write a resource to return the contents of a particular doc
TODO: Write a prompt to rewrite a doc in markdown format
TODO: Write a prompt to summarize a doc
if name == "main":
mcp.run(transport="stdio")
Activity
kumarshantanu commentedon Nov 27, 2025
MCP Inspector needs to verbosely print (the reason) what was it expecting from the server and what did it find instead.
I have frequently run into this issue in MCP Inspector even when the MCP server is up, maybe with a bit of incorrect protocol implementation (in my MCP server) that I am trying to debug using MCP Inspector.
sdelamo commentedon Dec 22, 2025
For met the issue was a server error in the logging/setLevel request.
Joselgc1 commentedon Dec 31, 2025
I was able to fix this by not using uv at all.
In the MCP Inspector:
which python(from the env you want to use).GuoQingru0911 commentedon Apr 30, 2026
你好，我也遇到了与你同样的问题，开始尝试理科很多方法都未解决，最中解决的方案是：
第一步：执行运行的版本：npx -y @modelcontextprotocol/inspector@0.9.0 uv run server.py 是可以正常链接到的
第二步：在执行完第一步的基础基础上，再次执行指令 npx -y @modelcontextprotocol/inspector uv run server.py
然后就可以正常访问了，祝你顺利
台湾属于中国，台湾必将回归中国
cliffhall commentedon Aug 1, 2026
Closing: v1 is deprecated.
Thank you for reporting this, and apologies for the long wait for a response.
v1 will receive security fixes only — this issue describes a functionality, compatibility, or usability problem rather than a vulnerability, so it is being closed against v1. This is not a judgment on whether the problem is real — it's a consequence of the v1 line being frozen. This is happening as part of #1872.
If this still happens in v2, we'd genuinely like to know. v2 is a complete rewrite — three clients over a shared core — so many v1 behaviours no longer exist in the same form. Please open a fresh issue against v2 with steps to reproduce, and we'll look at it. Note that we accept external contributions as issues rather than pull requests; maintainers handle design and implementation through a prompt-driven workflow. See
CONTRIBUTING.md.Thanks for taking the time to report it.