Kalendis is an API-first scheduling backend. You keep your UI; we handle the gnarly parts (recurrence, time zones, DST, conflict-safe bookings).
What it does: • MCP tool: generates typed clients and API route handlers (Next.js/Express/Fastify/Nest) so you can scaffold calls straight from your IDE/agent tooling. • Availability engine: recurring rules + one-off exceptions/blackouts, returned in a clean, queryable shape. • Bookings: conflict-safe endpoints for creating/updating/canceling slots.
Why we built it: We kept rebuilding the same "hard parts" of scheduling: time zones/DST edge cases, recurring availability, conflict-aware booking, etc. We wanted a boring, reliable backend so we could ship product features without adopting a hosted scheduling UI.
How it's helped: We stopped re-implementing DST/recurrence math and shipped booking flows faster. One small team (just 2 developers) built a robust booking platform for their business using Kalendis—they kept full control of their UX without spending lots of cycles on scheduling infrastructure. The MCP generator cut the glue code: drop in a typed client or route, call the API, move on.
Some tech details: • REST API with ISO-8601 timestamps and IANA time zones • Recurring availability + one-off exceptions (designed to compose cleanly) • Focused scope: users, availability, exceptions, bookings (not a monolithic suite)
The MCP server exposes tools like generate-frontend-client, generate-backend-client, generate-api-routes, and list-endpoints. Add to your MCP settings:
{
"mcpServers": {
"kalendis": {
"command": "npx",
"args": ["-y", "@kalendis/mcp"]
}
}
}
curl -H "x-api-key: $KALENDIS_API_KEY" \
"https://api.kalendis.dev/v1/availability/getAvailability?userId=<user-id>&start=2025-10-07T00:00:00Z&end=2025-10-14T00:00:00Z&includeExceptions=true"
Cool! Who is this for? Can you share some potential use cases? Do you have a clear understanding of your target audience? Or is this more of a “build it and they will come” approach?
Great questions. It's targeted at dev teams wanting to build their own custom experiences on the frontend without having to deal with the complications of a scheduling backend. This could be anything from calendar functionality in their application to a platform that handles bookings for an office, etc. While assisting several startups get their product built, we ran into a need for something like this which drove us to build this as a standalone service. Figured others might find it useful as well!
Why didn't you use something like Acuity? Serious questions because I'm building on their API right now (https://developers.acuityscheduling.com/).
Acuity is certainly a good option. We ultimately built our own because we knew it would be an on going feature we would need in the businesses that we were helping and we wanted to be able to own the stack ourselves. For long term cost savings as well as control over features that could be added in the future.
What’s the value prop of this over cal.com scheduling backend with higher primitives?
Good question. Currently the value here is cost vs api usage compared to something like cal.com. Similar usage there would be significantly higher. That said, they also have some additional features that we don't have yet. We are actively working towards new features to close the gap! Thanks for checking it out.
Date math as a service!
:D