Developer MCP Obsidian connector works in one Project but fails in another

ChatGPT Apps SDK
1

Hi everyone,

I’m using a custom Developer MCP connector for Obsidian. The connector works correctly in some ChatGPT chats and in at least one ChatGPT Project, but fails in another Project.

Connector details

The connector is an Obsidian vault connector running as a Developer MCP / custom app.

It exposes tools such as:

  • obsidian_list_notes
  • obsidian_global_search
  • obsidian_read_note
  • obsidian_update_note
  • obsidian_search_replace
  • obsidian_delete_note

The app is in development mode.

Expected behavior

I expected the same Obsidian connector to be available and callable in all Projects where Developer MCP / custom apps are supported.

In the working Project, ChatGPT can list, search, read, and update Obsidian notes.

Actual behavior

In another specific Project, the same connector either does not appear at first or fails when ChatGPT tries to call it.

When ChatGPT tries to call:

/Obsidian/obsidian_list_notes

I get this error:

FORBIDDEN: This conversation does not support developer MCPs

Google Drive and Google Sheets work in the same problematic Project, so this seems specific to Developer MCP support rather than all connectors.

My question

Is Developer MCP support controlled per Project, per chat, per workspace, or by Project type?

Can an existing Project be updated to support Developer MCPs, or do I need to create a new Project?

Also, are there known limitations when a Project uses custom instructions, custom GPT/Gizmo configuration, or other tools that prevent Developer MCP connectors from being used?

Any guidance or workaround would be appreciated.

2

Welcome to the community @arsenynn and thanks for laying this out clearly. This one’s definitely confusing.

That error usually means the conversation context does not allow Developer MCPs, even if the Project can use normal connectors like Drive or Sheets. So yes, this can behave differently by Project/chat type, not just by workspace.

Practical workaround: create a fresh Project/chat where the Developer MCP appears, then move the relevant instructions/files over. Existing Projects may not always “upgrade” cleanly into MCP-supported contexts.

Custom instructions or GPT/Gizmo-style setup can also be part of the issue if that Project is using a mode that doesn’t expose Developer MCP tools.

I’d test with:

  1. New blank Project
  2. Same model
  3. No extra tools/instructions
  4. Add only the Obsidian MCP

If that works, the original Project is likely locked into an unsupported configuration.

Curious if recreating the Project fixes it for you.

-Mark G.