ChatGPT
Turn on developer mode in ChatGPT and add WhyVault as an MCP server – so every chat can read and update your memory.
Guide as of 26 September 2026. Tested with the OAuth flow ChatGPT uses.
ChatGPT adds your own MCP servers via developer mode. It's available on Plus, Pro, Business, Enterprise and Edu – not on the free plan – and only on chatgpt.com in the browser.
Requirements
- ChatGPT plan: Plus, Pro, Business, Enterprise or Edu. The free plan has no developer mode.
- Where: chatgpt.com in a desktop browser. You set up the connection there; the ChatGPT apps for desktop and phone don't offer developer mode.
- Workspace: On Business, Enterprise and Edu an admin decides whether members may use developer mode. If the switch is missing, ask your admin first.
- WhyVault: any account, Free included. You don't need an access key – ChatGPT signs in via OAuth.
- Your MCP address:
https://mcp.whyvault.io– the same for everyone. You also find it in the app under Connect agents.
Set up developer mode and WhyVault
Turn on developer mode
On chatgpt.com, open Settings → Security and login and turn on Developer mode. On Business, Enterprise and Edu an admin may have disabled it.
ChatGPT warns you that developer mode allows tools that can change data. That's exactly what WhyVault needs: your agent should not only read but also write back what was decided.
Add WhyVault
Go to chatgpt.com/plugins, click +, name the app WhyVault, enter https://mcp.whyvault.io as the URL, choose OAuth as authentication and create the app.
Enter the address exactly like this – without a path such as /mcp or /sse and without a trailing slash. WhyVault speaks Streamable HTTP; ChatGPT detects that by itself.
Sign in and use it in a chat
Sign in in the WhyVault window and approve access. Then add WhyVault to a new chat from the tools menu. ChatGPT asks you to confirm each time before it writes to your vault.
A good first prompt:
Read my WhyVault and tell me in three sentences what I'm working on right now.ChatGPT should call vault_overview first and then search_notes or read_note. In WhyVault, the connection now shows up under Connect agents with the name ChatGPT registered.
Troubleshooting
The developer mode switch is missing
- You're on the free plan. Developer mode starts with Plus.
- You're in the ChatGPT app for desktop or phone. Open chatgpt.com in the browser.
- You're in a Business, Enterprise or Edu workspace and an admin hasn't allowed developer mode. Only the admin can change that in the workspace settings.
- Switch the workspace (top left) if you have both a personal and a company account – the setting applies per workspace.
The sign-in window doesn't open
ChatGPT opens WhyVault in a pop-up. If nothing happens, your browser is probably blocking pop-ups for chatgpt.com. Allow them and try again. Privacy extensions that block third-party windows can have the same effect.
The sign-in link opens in a different browser
WhyVault signs you in with a link by email. If your mail app opens it in another browser, the sign-in window in ChatGPT stays empty. Instead, type the code from the email in the sign-in window, or sign in with your password if you set one.
Creating the app fails
- Check the address:
https://mcp.whyvault.io, nothing more. - Choose OAuth, not "No authentication". Without sign-in, WhyVault answers every request with
401– that's intended and points ChatGPT to the sign-in. - If you denied access in the sign-in window, start again: delete the app in ChatGPT and add it once more.
WhyVault doesn't show up in the chat
Developer mode tools are not switched on automatically. Open a new chat, open the tools menu and pick WhyVault. If it's not in the list, check under chatgpt.com/plugins that the app exists and is connected.
Write tools are missing
If ChatGPT can search but not create notes, the connection is set to read only in WhyVault. Change it under Connect agents → Permissions. delete_note only appears if you allowed deleting for this connection. ChatGPT loads the tool list when you connect; after a change, refresh the app in ChatGPT or remove it and add it again.
The connection suddenly stops working
You revoked the connection under Connect agents, or your sign-in expired. Reconnect the app in ChatGPT and sign in again. A new approval starts with read and write; deleting has to be allowed again.
"Too many changes in a short time"
WhyVault slows down a connection that writes an unusual amount per minute. Wait a minute and ask ChatGPT to combine changes, for example several points in one note.
FAQ
Does it work on the free ChatGPT plan?
No. ChatGPT only adds your own MCP servers through developer mode, which starts with Plus.
Why does ChatGPT ask before every write?
That's ChatGPT's safety rule in developer mode. You see what it wants to write and confirm. In WhyVault every change also lands in the history, and you can undo it.
Does this replace ChatGPT's own memory?
No, both exist side by side. ChatGPT's memory stays in ChatGPT. Your vault belongs to you, and Claude, Cursor or Claude Code read the same notes.
What does OpenAI see?
Whatever ChatGPT reads from your vault is processed by OpenAI. WhyVault itself is EU-hosted (Frankfurt) and GDPR-compliant. Details: History, export and privacy.
Can I limit what ChatGPT may do?
Yes. Under Connect agents you set per connection whether ChatGPT only reads, also writes or may delete.