OneCal Calendar MCP Server

3. Give the client a recognizable name, for example: "ChatGPT". This helps you identify which app the client belongs to later.

4. LeaveSupports client-secret OAuth authenticationenabled.

5. Choose the scopes you want to grant. Scopes control what ChatGPT can do through the MCP server. For full calendar access, enableRead your calendar eventsandCreate and modify calendar events. Profile, email, and offline access are required and always included. Only grant the scopes you actually need.

6. In theDefault Redirect URIfield, paste theCallback URLyou copied from ChatGPT's Advanced OAuth settings.

Create the MCP client in OneCal and paste ChatGPT's callback URL

7. ClickCreate Client. OneCal will generate your client credentials, including theClient ID,Client Secret, and other connection details.

8. Copy and securely store these values. Treat theClient Secretlike a password. It is shown once and should never be shared publicly.

1. Go back to the ChatGPT app you started in Step 1, in theAdvanced OAuth settingssection.

2. Paste theClient IDandClient Secretfrom OneCal into their matching fields.

3. Acknowledge ChatGPT's custom MCP server warning by checkingI understand and want to continue, then clickCreate.

Authorize ChatGPT to access your OneCal account

6. After authorizing, ChatGPT redirects back and marks the app as connected.

Once connected, you can call the OneCal app in a conversation by typing@followed by the app's name (for example,@OneCal MCP) and then your request. For example, you can ask ChatGPT to:

- List your connected calendars.
- Check your availability for a given day or time range.
- Create, update, or delete calendar events.

ChatGPT will only be able to perform actions allowed by the scopes you selected when creating the client.

- Authorization fails or redirects to an error page:Make sure the redirect URI you added in OneCal exactly matches the Callback URL from ChatGPT's Advanced OAuth Settings. Even a trailing slash difference will cause the flow to fail.
- App can read but cannot create or edit events:Confirm you granted the calendar write scope when creating the client. You can edit the client's scopes inSettings > MCP Config.
- Invalid client errors:Double-check that theClient IDandClient Secretwere copied correctly, with no extra spaces.

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