OpenCalendar

Try the live demo → (fake calendar, resets daily) ·

The open-source Calendly alternative that AI agents can book. Self-hosted: one Next.js app that reads your real Google Calendar, takes bookings from any website or social bio, charges with Stripe when you want it to, and never loses or double-books a meeting.

Any AI agent that finds your site can book you. OpenCalendar publishes /llms.txt and a public, keyless MCP server, so an assistant like Claude or ChatGPT can see what you offer, check your real availability and book a free call for the person it works for. For a paid meeting the agent gets a checkout link with the time already picked, and a human pays.

Why it exists: booking links are revenue infrastructure. If one breaks quietly you lose calls you'll never know about. OpenCalendar is built around that: every booking is claimed under a database lock against your live calendar, every side effect is retried from a durable outbox, and anything that goes wrong shows up as an alert, not a log line.

What you get

• Agent-bookable — any AI agent can find you through /llms.txt and book the event types you opt in over a public, keyless MCP endpoint. Free meetings book straight through the same double-booking-safe path as a human; paid ones hand back a checkout link for a person to pay.
• Booking links — free or paid, one or several durations, Google Meet / Zoom link / phone / in-person / custom locations, up to 10 questions of six types, guests, single-use links, secret links.
• Availability like Calendly — named schedules, date overrides, start-time increments, buffers before and after, minimum notice, rolling calendar-day or business-day windows, fixed date ranges, daily and weekly limits, a pause switch, and a "why is this time not offered?" troubleshooter.
• Any number of calendars checked for conflicts; pick which one bookings are written to.
• Invitee self-service — reschedule and cancel links, with an optional enforced cutoff (Calendly only lets you write a policy) and automatic refunds by policy.
• Paid bookings — Stripe card form inline on the page (Apple/Google Pay, Link), slot held while they pay, safe on a Stripe account shared with other apps.
• Emails — confirmation, host notification, reminders (any offsets), follow-up, reschedule and cancellation notices, all branded per site.
• Embed anywhere — one script tag for popup, inline, or floating badge; plain links and iframes; a React component; a link-in-bio page per brand with share images; QR codes. Swapping from Calendly can be a one-line change.
• Brands — run several sites from one install, each with its own name, logo, colors and profile page.
• Webhooks, REST API and an MCP server — so Zapier, your CRM, or your own AI agent can read your availability and manage your bookings.
• Analytics — views → time picked → booked, by source, plus revenue, cancellations and no-shows. No cookies, no trackers.
• Your data, your database. No accounts, no vendor, no per-seat pricing. MIT licensed.

Let AI agents book you

1. Tick "AI agents can book this" on the event types agents may book (off by default; secret types are never exposed).
2. That's it. Agents discover you at https://your-instance.example.com/llms.txt and /.well-known/mcp.json, and connect to https://your-instance.example.com/api/mcp/public with no API key.

claude mcp add --transport http rivera-studio https://your-instance.example.com/api/mcp/public
# then: "book me a 30 minute intro with Rivera Studio next Tuesday afternoon"

Try it against the demo right now, no install: point any MCP client at https://opencalendar-demo.vercel.app/api/mcp/public, or read what an agent sees at opencalendar-demo.vercel.app/llms.txt.

Agent bookings go through the same lock and live calendar check as a human booking, send the same confirmation email and invite, are rate limited per IP and capped at one upcoming booking per email, and show up in admin tagged "via AI agent". Point your own site's llms.txt at your instance's so agents reading your site find it. Details: docs/MCP.md.

Screenshots

Popup embed. One script tag; opens instantly because it preloads.	Inline embed. Sizes itself to its content and takes each brand's colors.
Overview. System health, today's calls, revenue, one-click pause.	Analytics. Views → time picked → booked, per event type and source.
Bookings. Search, filter, refund, reschedule, export CSV.	Event types. Price, durations, windows, buffers, questions, policies.
Share. Every embed snippet, a UTM builder and a QR code.	Mobile. Built for traffic from social bios.

Admin screenshots use made-up demo data.

Self-host in ~20 minutes

You need Postgres, a Google account, somewhere to run Next.js (Vercel works), and Stripe only if you charge.

git clone https://github.com/nchemb/opencalendar.git && cd opencalendar
npm install
npm run setup     # writes .env, starts local Postgres, migrates, seeds, tells you what's missing
npm run dev

Open http://localhost:3000/admin (the password is in .env), then:

1. Google Calendar. In the Google Cloud console: enable the Google Calendar API, create an OAuth consent screen (Internal on a Google Workspace skips verification; on Gmail choose External and add yourself as a test user), then Credentials → OAuth client ID → Web application with redirect URIs http://localhost:3000/api/google/callback and https://<your-domain>/api/google/callback. Put the client ID and secret in .env, then Admin → Settings → Connect Google Calendar and choose which calendars count as busy.
2. Email (strongly recommended). A Resend API key and a verified from-address in RESEND_API_KEY / RESEND_FROM.
3. Alerts. Set ALERT_WEBHOOK_URL to a Slack or Discord webhook or an ntfy topic to get pushed to your phone when anything needs you.
4. Stripe (paid types only). STRIPE_SECRET_KEY, NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY, and a webhook to https://<your-domain>/api/stripe/webhook for checkout.session.completed, checkout.session.expired and payment_intent.succeeded with its secret in STRIPE_WEBHOOK_SECRET.
5. Scheduler. Call /api/cron/tick every 5–10 minutes with Authorization: Bearer $CRON_SECRET — retries, reminders and health checks run there. The included vercel.json does it on Vercel Pro; see docs/RELIABILITY.md for GitHub Actions, cron and uptime-monitor options.

Deploy: use the Deploy with Vercel button at the top (it asks for the required variables; migrations run on every Vercel production build), or push to GitHub, import into Vercel, copy every variable from .env (watch for trailing whitespace in pasted secrets, a classic silent-401), set NEXT_PUBLIC_APP_URL and GOOGLE_REDIRECT_URI to your domain, and reconnect Google once from the deployed admin. Use a Postgres that never pauses: a free database that sleeps after a week idle will take your booking pages down with it.

Coming from Calendly? npm run import:calendly -- https://calendly.com/<you> copies your event types, questions, prices and hours. See docs/MIGRATE-FROM-CALENDLY.md.

Admin password

/admin has one owner login: the ADMIN_PASSWORD environment variable. npm run setup generates a random one, prints it once and saves it in .env; in production set it in your host's env vars. There is no "forgot password" email on purpose: whoever can change the env var owns the instance, so recovery is "set a new ADMIN_PASSWORD and redeploy". The password also signs the session cookie, so changing it logs out every browser (so does Log out everywhere).

Put it on your site

<script src="https://<your-domain>/embed.js" defer></script>

<!-- popup -->
<button data-bookkit-popup="strategy-call">Book a call</button>

<!-- inline, sizes itself to its content -->
<div data-bookkit-inline="strategy-call"></div>

The project was called BookKit before it was renamed, so the embed API keeps that name (window.BookKit, data-bookkit-*, bookkit:* events, the BookKit-Signature webhook header and BOOKKIT_* env vars). Existing embeds keep working.

Social bio: link to https://<your-domain>/u/<brand>. Everything else (badge, React, Webflow, WordPress, Framer, Squarespace, email signature, analytics events) is in docs/EMBED.md. The API is in docs/API.md, webhooks in docs/WEBHOOKS.md, and AI-agent booking over MCP in docs/MCP.md.

How it stays correct

Every row has tests behind it (npm test runs them against a real Postgres).

Risk	What stops it	Tests
Two people book one slot	The claim runs in a Serializable transaction holding a per-host pg_advisory_xact_lock, re-checks DB overlaps, limits and live free/busy on every conflict calendar, then inserts. One wins; the rest get a clean 409.	concurrency, v2-booking
A calendar is unreadable	Fails closed: no slots shown, no bookings taken. An error on any one conflict calendar counts.	calendar-failure, google-auth
Calendar write fails after the slot is claimed	The booking stays confirmed (it's the invitee's slot), a calendar.create job retries with backoff, and you get a critical alert until the event lands.	calendar-failure
An email, webhook, reminder or refund fails	Everything after the booking row is a job in a durable outbox, claimed with SKIP LOCKED, retried with backoff, and turned into an alert if it finally dies. Nothing is dropped silently.	v2-booking, v2-ops
Payment lands on a slot someone else took	Hold (33 min) outlives the Stripe session (31 min). If it still happens: automatic refund, apology email, alert.	paid-booking
A Stripe webhook is late, duplicated, forged, or from another app on the same account	Signature-verified; claimed once with a conditional update; ignored unless it matches an object OpenCalendar created; and the booking page and cron pull payment status from Stripe, so a missing webhook never strands a payer.	stripe-webhook, paid-booking, v2-booking
An abandoned hold burns a slot	Holds expire lazily and are swept inside the booking lock and by the cron — including holds that died before payment ever started.	paid-booking, v2-ops
Your booking page silently offers nothing	A canary checks every public link can read the calendar and has open times; you're alerted if not. /api/health returns 503 for uptime monitors.	v2-ops
You delete or move a booked meeting in Google by hand	Reconcile notices and alerts you with the booking, so the invitee gets told.	v2-ops
DST and timezones	Stored in UTC; wall-clock maths in the schedule's zone via Luxon, including the spring-forward and fall-back days themselves.	slots
Someone forges an admin session	HMAC-signed cookie over expiry + session version; "sign out everywhere" revokes every issued cookie.	admin-auth

Commands

npm run setup            # first run
npm run dev
npm run build
npm test                 # unit + integration (needs Postgres: npm run db:up)
npm run test:e2e         # Playwright against a production build
npm run import:calendly -- https://calendly.com/<you> --dry-run

No test needs a Google account, a Stripe account, or the network — see CONTRIBUTING.md.

Adding a calendar backend

Everything talks to calendars through CalendarPort (lib/calendar-types.ts): free/busy, create, update, delete, get, list. Google and an in-memory backend ship; Outlook or CalDAV is one file plus a line in lib/calendar.ts.

Not included

Round robin, collective and team scheduling, group events, meeting polls, SMS. OpenCalendar is a tool for one person running one or more brands. If you need teams, Cal.com is open source and does them well.

Contributing

See CONTRIBUTING.md. Security issues: SECURITY.md.