June 22, 2026 · 5 min read

How to create a ChatGPT Custom GPT that sets reminder calls

Import the ReminderIt OpenAPI spec into a ChatGPT Custom GPT and ask your AI to schedule a phone call in plain English.

ChatGPT Custom GPTs let you build a specialised version of ChatGPT with access to external APIs via Actions. ReminderIt provides a ready-made OpenAPI spec that covers your full account — creating reminders, checking usage, managing recipients, and more. Here's how to set it up in under ten minutes.

Step 1: get your ReminderIt API key

New to ReminderIt? Message https://wa.me/14786061901 on WhatsApp to start a 7-day free trial. Then log in at reminderit.com with WhatsApp or Google and create an API key as described at reminderit.com/developers/api. Label it 'ChatGPT' and copy the rmt_... key for step 3.

Step 2: open the GPT builder

In ChatGPT (Plus or Team), go to Explore GPTs → + Create. Click the Configure tab. Give your GPT a name ('My Reminder Assistant') and a description like 'Manages my ReminderIt phone call schedule'.

Step 3: add the ReminderIt action

Click Add Action. In the 'Import from URL' field paste: https://reminderit.com/openapi.yaml — the schema loads automatically.

For Authentication, select API Key. Set Auth Type to Custom. Header name: X-API-Key. Value: your rmt_... key. Click Save.

Step 4: test it

Back in the Preview panel, ask: "Create a daily wake-up call at 7am New York time." The GPT will call the ReminderIt API and confirm the reminder. At 7am your phone rings and a WhatsApp message arrives with Done and Snooze.