openslot

Open-source scheduling that just works. No account. No paywall. No subscription. Set your availability. Share your link. Let people book time with you -- with automatic Google Meet, email reminders, and rescheduling built in.

Live Demo →

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What It Does

You share a link. Someone picks a time. You both get a calendar invite with a Google Meet link, a confirmation email, and automatic reminders before the meeting.

If they need to reschedule or cancel, they can do that too -- no account required, no back-and-forth emails.

That's it.

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Why Not Just Use Calendly?

Calendly's free tier locks the features people actually use behind a $20/month paywall.

Feature	Calendly Free	Calendly Standard ($20/mo)	openslot
Google Calendar sync	✅	✅	✅
Google Meet auto-link	❌	✅	✅
Email confirmations	✅	✅	✅
24h + 1h reminders	❌	✅	✅
Rescheduling flow	❌	✅	✅
Cancellation flow	❌	✅	✅
ICS calendar attachment	❌	✅	✅
Disposable email blocking	❌	❌	✅
No-login manage links	❌	❌	✅
You own your data	❌	❌	✅
Monthly cost	$0	$20	$0 forever

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Everything Included

Booking

• Two meeting types -- 30-minute deep dive and 15-minute quick chat
• Smart slot generation with buffer time and conflict detection
• Blocks disposable email addresses at input

Calendar

• Creates Google Calendar events automatically
• Attaches a Google Meet link to every booking
• Downloads an .ics file so guests can add it to any calendar app

Emails

• Confirmation email sent immediately on booking
• Reminder emails 24 hours and 1 hour before the meeting
• Cancellation email if the meeting is cancelled -- reminders auto-cancelled too

Rescheduling & Cancellation

• Every confirmation email includes a secure manage link
• Guests reschedule or cancel without creating an account
• Links are HMAC-signed -- tamper-proof, no auth system needed

Reliability

• 62 tests covering slot generation, validation, reminders, and availability
• Timezone-aware scheduling using Luxon
• Full conflict detection via Google Calendar freebusy API

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How It Works

Guest picks a time → Booking confirmed
                          ├→ Google Calendar event created (+ Meet link)
                          ├→ Confirmation email sent (with ICS attachment)
                          └→ Reminders scheduled (24h + 1h before)

Guest clicks manage link → Verified via HMAC token
                          ├→ Reschedule → new time, updated calendar event, new emails
                          └→ Cancel → event deleted, cancellation email, reminders cancelled

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Tech Stack

• Next.js 14 (App Router)
• TypeScript
• Google Calendar API
• Resend (transactional email + reminder scheduling)
• Luxon (timezone-aware date handling)
• Vitest (62 tests)

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Self-Host in 15 Minutes

Prerequisites

• Node.js 18+
• Google Cloud project with Calendar API enabled
• Google service account with calendar access
• Free Resend account

1. Clone & Install

git clone https://github.com/yourusername/openslot.git
cd openslot
npm install

2. Set Environment Variables

# Google Calendar
GOOGLE_SERVICE_ACCOUNT_EMAIL=your-service-account@project.iam.gserviceaccount.com
GOOGLE_PRIVATE_KEY="-----BEGIN PRIVATE KEY-----\n...\n-----END PRIVATE KEY-----\n"
GOOGLE_CALENDAR_ID=your-calendar@gmail.com
GOOGLE_CALENDAR_TIMEZONE=America/New_York
GOOGLE_OAUTH_CLIENT_ID=
GOOGLE_OAUTH_CLIENT_SECRET=
GOOGLE_OAUTH_REDIRECT_URI=
GOOGLE_OAUTH_REFRESH_TOKEN=

# Resend
RESEND_API_KEY=re_...
RESEND_FROM_EMAIL=Bookings <bookings@yourdomain.com>

# Booking
BOOKING_ADMIN_EMAIL=you@example.com
BOOKING_SIGNING_SECRET=your-random-hex-string
NEXT_PUBLIC_BOOKING_TIMEZONE=America/New_York

3. Run

npm run dev

4. Test

npm test

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Project Structure

src/
├── lib/
│   ├── google-calendar.ts    # Slot generation, availability, event CRUD
│   ├── google-auth.ts        # Google OAuth + service account auth
│   ├── booking-email.ts      # HTML/text email templates
│   ├── schedule-reminders.ts # Resend scheduled reminders (24h + 1h)
│   ├── booking-ics.ts        # ICS calendar file generation
│   ├── booking-token.ts      # HMAC token generation/verification
│   ├── calendar-utils.ts     # Helpers for extracting calendar event data
│   ├── validation.ts         # Server-side email validation (disposable domain checks)
│   ├── validation-client.ts  # Client-safe validation (name, agenda, LinkedIn URL)
│   └── __tests__/            # 62 tests across 5 test files
├── app/
│   ├── api/calendar/
│   │   ├── availability/     # GET available slots
│   │   ├── book/             # POST create booking
│   │   ├── manage/           # GET verify token + booking details
│   │   │   └── availability/ # GET slots for rescheduling
│   │   ├── reschedule/       # PUT reschedule booking
│   │   └── cancel/           # DELETE cancel booking
│   └── book/
│       ├── page.tsx          # Booking form UI
│       ├── manage/page.tsx   # Reschedule/cancel UI
│       └── layout.tsx        # Booking layout
└── components/ui/
    └── BackButton.tsx

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Contributing

Found a bug or missing feature? PRs welcome.

Open an issue describing what you hit and what you expected.

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License

MIT