mcp-remote no longer able to connect

[TheXenocide]

The README.md contains directions for clients that don't support Streamable HTTP yet, but those directions are no longer valid. It seems some form of data protection is blocking requests (I tried another node-based http->stdio adapter but had the same issue).

stderr: [70012] Connection error: Error: Error POSTing to endpoint (HTTP 500): The key {a92859ef-53e3-497c-a0dd-2daa2da44557} was not found in the key ring. For more information go to https://aka.ms/aspnet/dataprotectionwarning

After a bit of an adventure on the interwebs I did eventually manage to find mcp-proxy (python based instead of node.js) and some explicit arguments which did the trick. After using uv tool install mcp-proxy I was able to get things up and running in LM Studio with the following configuration:

{
  "mcpServers": {
    "microsoft.docs.mcp": {
      "command": "mcp-proxy",
      "args": [
        "--transport",
        "streamablehttp",
        "https://learn.microsoft.com/api/mcp/"
      ]
    }
  }
}

[mhawthorne-nip]

I am getting this from VSCode and Claude code.

[jesegher]

+1 Connection state: Error 500 status sending message to https://learn.microsoft.com/api/mcp: The key {c7d253c6-ed2c-4985-8e18-c30551ef7159} was not found in the key ring.

[pdebruin]

I am getting this from VSCode and Claude code.

Hi @mhawthorne-nip, you shouldn't need mcp-remote or mcp-proxy from VSCode of Claude Code, since both can talk to remote MCP directly. Can you elaborate?

[pdebruin]

@TheXenocide @jesegher, can you share more about your environment? OS, MCP client, anything else relevant. The mcp-remote option still works for me.

[jesegher]

hi @pdebruin just tested this morning and got one query to work. After the first query, I got this

System: Windows 11 Copilot + PC
Client: VS Code + Insider

With the changes made for MCP Proxy, it ran perfectly.

[jesegher]

@pdebruin I tried it again .. It connected. It found the MCP Tool and when executed, cancelled the connection

[pdavis68]

I can't get it working in Cline. It either gives me errors starting up or it can't find any tools listed.

I set it up in MCP Inspector and it throws 500 errors a lot, but if you keep retrying, it'll eventually work. But Cline won't be this persistent. They need to fix the service, obviously.

[mhawthorne-nip]

I am getting this from VSCode and Claude code.

Hi @mhawthorne-nip, you shouldn't need mcp-remote or mcp-proxy from VSCode of Claude Code, since both can talk to remote MCP directly. Can you elaborate?

This is my Claude Code config:

"microsoft.docs.mcp": {
"type": "http",
"url": "https://learn.microsoft.com/api/mcp",
"args": [],
"env": {}
}

This is what I get:

debug": "HTTP Connection error: {"url":"https://learn.microsoft.com/api/mcp\",\"error\":\"Error POSTing to endpoint (HTTP 500): The key {83e8a517-600e-4af6-a325-99004cd1aa07} was not found in the key ring. For more information go to https://aka.ms/aspnet/dataprotectionwarning\"

"error": "Error: Error POSTing to endpoint (HTTP 500): The key {83e8a517-600e-4af6-a325-99004cd1aa07} was not found in the key ring. For more information go to https://aka.ms/aspnet/dataprotectionwarning\n

[partychen]

@TheXenocide @jesegher @mhawthorne-nip Thank you for reporting this issue.

Interestingly, I haven’t been able to reproduce it on my local environment — whether using a remote URL directly or going through the mcp-proxy, it consistently works. I even suspected it might be related to session changes, so I restarted the backend service. It did report Connection state: Error; will retry with new session ID, but still ended up succeeding afterward.

Do you happen to have a reliable way to reproduce this issue consistently?

I did come across this related SDK issue:
modelcontextprotocol/csharp-sdk#484
However, I’m not entirely sure if it’s the same root cause. Without a consistent repro on my end, it's quite difficult for me to investigate or apply a fix with confidence.

======================================
Based on my observations, I can currently use MCP without issues. However, when I restart the backend service to simulate a lost session, the MCP server in VS Code still shows as "started." If I then send a request, I receive this message:
Connection state: Error; will retry with new session ID,But the request does not succeed.
Interestingly, clicking the "+" button in the top-right corner to start a new chat refreshes the session ID, and the MCP server resumes normal operation. Restarting either the MCP server or VS Code also resolves the issue.

Possible underlying mechanism:
The MCP client (such as the VS Code extension) maintains a long-lived connection or persistent session. When the backend service restarts, it loses the previous session ID.

At this point, client requests fail and log Connection state: Error. However, the client does not proactively discard the old session ID. Only by manually creating a new chat or refreshing the client state is a new connection fully established.

The log message will retry with new session ID appears to be an expected behavior description, but in practice, the client does not automatically switch to a new session ID.

[partychen]

Regardless, I’m implementing a fix that will renew the session ID on the server side. Once it’s released, I’ll provide an update here.

[pdavis68]

@partychen
I'm confused. These are 500 errors, indicating a server-side issue. So why would you, necessarily have to reproduce it? Can you not spot the failure in the logs? I just got it now:

MCP error -32001: Error POSTing to endpoint (HTTP 500): The key {83e8a517-600e-4af6-a325-99004cd1aa07} was not found in the key ring. For more information go to https://aka.ms/aspnet/dataprotectionwarning

I'm using a tool called MCP Inspector to try figure out what's going on.

I was able to Initialize, get a tool list, but then when I called the tool, I got this error. It fails roughly 50% of the time.

This is fine for a tool like MCP Inspector, but these repeated failures don't work with my dev tools. They won't keep retrying.

[partychen]

@pdavis68 Thank you for your information! This 500 error is thrown by the .NET SDK of MCP and is related to DataProtection under the .NET Framework. If I can’t reproduce the issue locally, it’s difficult for me to fully understand why the error is being thrown. I’ve already set stateless = true, so it shouldn’t be related to session state — which makes me suspect there may be an issue within the SDK itself.

That said, I’ve already tried a potential fix — will be released tomorrow, would you mind kindly testing it on your side to see if it resolves the issue later?

I often use MCP Inspector to test our mcp server. Configure like below, is it different with you?

[mhawthorne-nip]

Here's an output from VS Code, if it helps at all. And yes it does work from mcp-inspector.

2025-07-02 10:15:58.430 [info] Starting server from LocalProcess extension host
2025-07-02 10:15:58.430 [info] Connection state: Running
2025-07-02 10:15:58.430 [debug] [editor -> server] {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{"roots":{"listChanged":true},"sampling":{}},"clientInfo":{"name":"Visual Studio Code","version":"1.101.2"}}}
2025-07-02 10:15:58.746 [debug] [server -> editor] {"result":{"protocolVersion":"2025-03-26","capabilities":{"logging":{},"tools":{"listChanged":true}},"serverInfo":{"name":"Learn.MCP.API","version":"1.0.0.0"}},"id":1,"jsonrpc":"2.0"}
2025-07-02 10:15:58.746 [debug] [editor -> server] {"method":"notifications/initialized","jsonrpc":"2.0"}
2025-07-02 10:15:58.747 [debug] [editor -> server] {"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}
2025-07-02 10:15:58.876 [debug] 405 status connecting to https://learn.microsoft.com/api/mcp for async notifications; they will be disabled:
2025-07-02 10:15:59.207 [info] Connection state: Error ; will retry with new session ID

And from Claude Code:

DEBUG] MCP server "microsoft.docs.mcp": No token data found
[DEBUG] MCP server "microsoft.docs.mcp": HTTP Connection error: {"url":"https://learn.microsoft.com/api/mcp","error":"Error POSTing to endpoint (HTTP 500): The key {a92859ef-53e3-497c-a0dd-2daa2da44557} was not found in the key ring. For more information go to https://aka.ms/aspnet/dataprotectionwarning","stack":"Error: Error POSTing to endpoint (HTTP 500): The key {a92859ef-53e3-497c-a0dd-2daa2da44557} was not found in the key ring. For more information go to https://aka.ms/aspnet/dataprotectionwarning\n at on1.send (file:///home/mph005/.npm-global/lib/node_modules/@anthropic-ai/claude-code/cli.js:1342:25035)\n at process.processTicksAndRejections (node:internal/process/task_queues:95:5)\n at async Ln1.notification (file:///home/mph005/.npm-global/lib/node_modules/@anthropic-ai/claude-code/cli.js:1336:19552)\n at async Ln1.connect (file:///home/mph005/.npm-global/lib/node_modules/@anthropic-ai/claude-code/cli.js:1336:21449)"}

[TheXenocide]

I ran into the issue in multiple tools but I think the first and likely easiest to repro was with LM Studio. I'll check again when I get home to be sure it's still occurring, though I also eventually had issues even with the mcp-proxy replacement.

I wonder if there are zone-based policies applied somewhere that are preventing the Data Protection policies from being applied to your connections (or mine)? I don't believe I was using one at the time, but I do occasionally have a VPN enabled; alternatively, if you have GSA/VPN it's possible MS allows you to do things we can't (or maybe it's only happening in some availability zones?)

--

ETA: I just set it up in LM studio on my machine in the office and the issue does not reproduce from here. I'll see if I can get some logs for you if I can repro.

[mhawthorne-nip]

Well it's actually working now, I am able to get documentation from it in Claude.