Cloud MCP Error: SSE error: Non-200 status code (400)

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1

Hi, I’m trying to use MCP Server via the cloud version at design.penpot.app/mcp/stream, but two systems are already telling me it’s unavailable—Error: SSE error: Non-200 status code (400)

I’ve tried Qwen Studio and Open WebUI

Is this a restriction because I’m using the free version?

2

Hi @GwynnBleiidd, the MCP is also available for the Penpot free version. Can you give me more information on what is going on?

3

Actually, not very many, but let’s give it a try

Qwen Studio—I add a server and immediately run into an error

image
image2352×1004 201 KB

Oh, and I can’t upload more than one image, so I’ll just have to describe it in words)

Open WebUI—a little better; the validation passes when adding. But when I try to communicate, it already reports issues - Failed to connect to MCP server ‘penpot’

Of course, I’ll try some more advanced tools tonight, like Codex, Claude Code, and extensions for VS Code

4

Hi @GwynnBleiidd :slight_smile:

You’re probably not doing anything fundamentally wrong, but:

  • either authentication is missing

  • or (more likely) the clients you’re using don’t fully support MCP over SSE

If you can share how you configured the server in Open WebUI (headers + auth), I can point out exactly what’s off.

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5

Everything worked out; I had forgotten that Qwen Studio requires a type in the JSON.

And with that object, everything started working—it was actually Google Antigravity that reminded me I had forgotten to add the type.

{
  "mcpServers": {
    "penpot": {
"type": "streamable-http",
      "url": "https://design.penpot.app/mcp/stream?userToken=token"
    }
  }
}
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