AvailEngine is a REST Booking API that gives you full control over scheduling workflows. Multi-tenant, scoped API keys, Stripe deposits, idempotent requests, and webhooks — without the UI lock-in.
No redirects, no iframes, no calendar UI imposed on you. Pure API infrastructure for your booking workflows.
Generate keys with granular permissions per tenant — read-only, write, admin. Revoke or rotate without downtime.
Each tenant gets isolated data, custom domains, and independent rate limits. Built for platforms and marketplaces from day one.
Accept deposits and full payments at booking time. Stripe integration is native — no separate payment setup required.
Retry safely with Idempotency-Key headers. Never accidentally double-book a slot or charge a customer twice.
Receive real-time events for booking.created, booking.cancelled, payment.succeeded, and more. Retry with exponential backoff.
Two-way sync with Google Calendar. Availability is always up to date, and booked slots block your calendar automatically.
MCP server and Claude Code plugin included. Build scheduling workflows from natural language in your editor.
Hosted on European infrastructure with GDPR compliance. Low-latency edge delivery worldwide.
Start free, scale as you grow. No hidden fees, no per-seat charges.
Other scheduling tools lock you into their UI. AvailEngine gives you a proper API from day one.
| Feature | AvailEngine | Calendly | Cal.com | Astrocal |
|---|---|---|---|---|
| REST API with curl-able endpoints | ✓ | ✗ | ✓ | ✓ |
| Scoped API keys | ✓ | ✗ | Partial | ✗ |
| Multi-tenant architecture | ✓ | ✗ | Via self-host | Via self-host |
| Stripe deposits built in | ✓ | ✗ | ✗ | ✓ |
| Idempotency-Key support | ✓ | ✗ | ✗ | ✗ |
| Webhooks with retries | ✓ | Limited | ✓ | ✓ |
| Google Calendar two-way sync | ✓ | ✓ | ✓ | ✓ |
| Free tier | €0/mo | Free | Free | $0/mo |
| Paid tier starts at | €129/mo | $16/seat | Open source | $199/mo |