Kalendis
Scheduling API (keep your UI, we handle timezones/DST)
Details
- External ID
- 45956154
- Source
- HN
- Company
- —
- Product
- Kalendis
- Website domain
- kalendis.dev
- Launched
- Nov. 17, 2025
- Cohort
- —
- Upvotes
- 18
- Upvotes percentile
- 0.6703056768558951
- Tags
- —
- Fetched at
- Sept. 7, 2026, 9:25 p.m.
- Updated at
- Sept. 7, 2026, 9:25 p.m.
Description
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"] } } } How to try it: Create a free account → get an API key. (https://kalendis.dev). Then hit an endpoint: 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" Happy to answer questions and post example snippets in the thread. Thanks for taking a look!
Enrichment
- Theme
- meeting scheduling and notetaking tools
- Vertical
- Horizontal
- Function
- Dev tools
- Audience
- Developer
- AI stance
- Not AI
- Project type
- Commercial product
- Normalized one-liner
- scheduling api handling timezones
- Manually corrected
- False
Could you build this?
Partial Building a basic scheduling UI or CRUD booking tool is trivial, but building a battle-tested scheduling engine handling complex recurrence (RRULE), timezones, DST shifts, and race-condition-free bookings is mathematically and architecturally tricky.
What it would actually take: A robust scheduling backend requires a distributed transaction-safe database schema (PostgreSQL with strict exclusion constraints), robust RFC 5545 recurrence calculation algorithms, and IANA timezone database sync. The core difficulty lies in atomic double-booking prevention under concurrent requests across arbitrary time boundaries and Daylight Saving Time shifts. Requires backend systems expertise in distributed concurrency and temporal logic.
Discussion
8 comments analyzed.
Competitors mentioned: Acuity Scheduling, cal.com
Concerns raised: Higher API usage costs compared to cal.com, Missing features that competitors have, Unclear target audience definition
Feature requests: Additional features to close gap with cal.com
Competitors
Other products that read as similar to this one — 20 launches clear the similarity bar, closest 8 shown.
Attention rank: #12 of 21 (itself plus its competitors, highest first — normalized so YC and Product Hunt are compared fairly).
Looks like the first mover among its competitors.
- cael · ph · 2026-09-25 · 2 upvotes · similarity 0.42
- Timezone App · hn · 2026-03-29 · 19 upvotes · similarity 0.40
- Kalendi · ph · 2026-09-13 · 1 upvotes · similarity 0.39
- FastScheduler · hn · 2026-01-13 · 46 upvotes · similarity 0.37
- Lightweight Task queue on Erlang/OTP, SQLite-backed, no overengineering · hn · 2026-06-10 · 75 upvotes · similarity 0.36
- kassette · hn · 2026-07-13 · 9 upvotes · similarity 0.34
- Time Keep · hn · 2026-03-19 · 26 upvotes · similarity 0.34
- Durable Endpoints · hn · 2026-02-18 · 8 upvotes · similarity 0.33
Other launches for this product
- No other launches for this product.
Same idea, different domain
Nobody's really built a dev tools tool for Sales yet.