# Daily Retell AI reminder calls for tomorrow's appointments > Every weekday at 8am, an AI voice agent calls tomorrow's customers with a friendly reminder, then posts a single Slack summary with the outcomes. - Workflow type: agent - Services: Retell AI, Google Calendar, Slack Bot - Categories: Operations, Sales - Published: 2026-07-08 ## What it does - Reads the next day's calendar every weekday morning and picks out real customer appointments with a phone number attached. - Places a friendly AI voice reminder call to each customer that mentions their name, appointment time, and location. - Listens to how each call went and separates confirmed reminders, voicemails, and customers who asked to reschedule. - Posts one grouped Slack summary to your team so a human can follow up on reschedules without listening to every call. ## What you'll need - A Google Calendar account with the calendar that holds your customer appointments. - A Retell AI account with a reminder voice agent and a phone number ready to place outbound calls. - A Slack workspace and the channel where the daily summary should be posted. - Appointments where the customer's phone number is on the attendee list, in the location field, or in the description. ## Prompt Build me an agent workflow that places friendly Retell AI reminder calls for tomorrow's customer appointments each morning and reports the outcome to my team in Slack. Trigger: cron, every weekday at 8am in my local time zone. Step 1. Use Google Calendar List Events to pull events from my target calendar in the next 24 to 36 hours. I want a slightly wider than 24-hour window so early-morning appointments on the far side of the boundary are not missed. Step 2. Have the agent filter that list down to genuine customer-facing appointments. Skip internal meetings, all-hands, focus blocks, all-day events, and anything without a phone number in the attendee list, location, or description. This is a judgment call, not a hard rule set, so let the agent reason over the event title, description, and attendees to decide. Step 3. For each qualifying event, extract the attendee's name, phone number, and appointment time. Normalize the phone number to E.164. If two events share a phone number, treat them as one customer with back-to-back appointments and only call once. Step 4. For each qualifying event, use Retell AI Create Outbound Phone Call with my reminder voice agent and my Retell phone number. Pass name, appointment time, and location as dynamic variables so the voice agent can speak them naturally. Keep the outbound calls spaced out enough to respect Retell's workspace concurrency, and record the call_id returned for each event so we can look up the outcome later. Step 5. After the batch is dispatched, wait a few minutes for the calls to complete. Then use Retell AI List Calls filtered to the time window of this run (or Retell AI Get Call for each recorded call_id) to pull the outcome, transcript, and call analysis for every call placed in this run. Step 6. Have the agent classify each call into one of three buckets based on the transcript and analysis: (a) reminded successfully, meaning a live person heard the reminder, (b) voicemail or no answer, (c) customer explicitly asked to reschedule. Step 7. Post a single Slack summary via Slack Bot Send a Message to my operations channel. Include the counts for each bucket (how many reminded, how many hit voicemail, how many reschedules) and then a named list of the customers who asked to reschedule with their original appointment time so a human can follow up. Also include a short list of events that were skipped because they had no phone number or looked internal, so nothing is silently dropped. Keep it one message, not one per call. Inputs I want to configure when I set this up: the source Google Calendar id, the Retell voice agent id, the Retell from-number, the Slack channel id for the summary, the local time zone for the 8am schedule, and an optional @mention for the ops lead when there are reschedules to handle. Failure handling: if Retell returns an error placing one call, log it and continue with the rest of the batch. If Google Calendar returns zero qualifying events, still post a short 'no reminder calls needed today' Slack message so the team knows the workflow ran. ## How to customize - Change when the reminders go out. Push them earlier for morning bookings or run a second pass in the afternoon for same-day changes. - Rewrite what the voice agent says. Match your brand tone, switch languages, or add specific prep instructions for the appointment. - Tighten which events count as customer appointments. Add rules to skip internal meetings, focus blocks, all-hands, or specific calendars. - Pick which Slack channel gets the summary and who gets @mentioned when a customer asks to reschedule. ## FAQ ### How much does this actually reduce no-shows? Reminder calls typically cut no-show rates roughly in half compared to no reminder at all, and they capture reschedule requests before the slot is wasted. The exact lift depends on your industry and how far in advance you call. ### What if an appointment does not have a phone number? It gets skipped and called out in the daily Slack summary so nothing is silently dropped. You can point the workflow at a linked CRM record if your numbers live somewhere other than the calendar event. ### Will customers know they are talking to an AI? That is up to you. The voice agent script is fully editable, so you can be upfront about it, keep it neutral, or route anything the agent cannot resolve to a human callback. ### Can I use my own Retell voice agent? Yes. Point the workflow at any published reminder agent in your Retell workspace. Name, appointment time, and location are passed in as dynamic variables so the agent speaks naturally. ### What happens if Retell fails to place one of the calls? The workflow logs the failure, keeps going with the rest of the batch, and lists the failed attempts in the Slack summary so your team can call those customers directly. Use this prompt in General Input: https://www.generalinput.com/prompts/daily-retell-ai-reminder-calls-for-tomorrows-appointments