Chronos

Automatic calendar scheduling for large groups

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Chronos

Chronos is a full-stack web application that automatically schedules meetings on Google Calendar for large groups. It achieves this by connecting to each participant's Google Calendar, analyzing availability across the group and ranking candidate time slots using a multi-factor scoring algorithm.

Live App: https://usechronos.live/

Alternate Link: https://chronos-ba69a.web.app/

Chronos v1 Launch: https://www.producthunt.com/products/chronos-11

Tech Stack

Frontend

React TypeScript Tailwind CSS Vite shadcn/ui Zustand Sonner

Backend

Python Firebase Functions Google Calendar API Resend Sentry

Infrastructure

Firebase Auth Firestore Firebase Hosting Google Cloud

Scheduling Algorithm

The algorithm lives in functions/scheduling/algorithm.py and runs inside the schedule_meeting Cloud Function.

Step 1: Collect availability

For each participant with a connected Google Calendar, the backend calls the Google Calendar FreeBusy API to fetch their busy intervals over the next 4 weeks.

Step 2: Compute the shared work window

Each participant stores their work hours (start/end time + timezone) and work days in Firestore. The algorithm:

  • Converts every participant's work hours to UTC using their timezone
  • Takes the latest start and earliest end across all participants as the shared window for each day
  • Takes the intersection of work days so only days everyone works are considered

Step 3: Find candidate slots

For each valid working day, the algorithm steps through the shared window in 15-minute increments. Each candidate slot is checked against all participants' busy intervals, expanded by each person's configured buffer time (default 15 minutes). A slot is only kept if it is conflict-free for everyone and starts at least 1 hour from now.

Step 4: Score each slot

Every passing slot receives three component scores:

Position score (15% of total score): The work window is divided into three equal thirds: morning, midday and afternoon. The score peaks at the center of the preferred third and decays linearly toward 0 at the opposite end.

Buffer score (15% of total score): Measures how much free time surrounds the slot for each participant. The gap between the slot and the nearest adjacent event on each side is measured and normalised to 0–1 (120 minutes of free time = full score of 1.0).

Proximity score (70% of total score): When the user specifies a target date, every slot receives a proximity score calculated as:

proximity = 1 / (1 + days_away_from_target)

Final score:

score = 0.7 * proximity_score + 0.15 * position_score + 0.15 * buffer_score

Step 5: Return ranked slots

The top 5 ranked slots are returned.

Getting Started

Prerequisites

1. Clone the repository

git clone https://github.com/Raghavsk24/Chronos.git
cd Chronos

2. Frontend environment variables

cp .env.example .env.local

Fill in .env.local:

VITE_FIREBASE_API_KEY=
VITE_FIREBASE_AUTH_DOMAIN=
VITE_FIREBASE_PROJECT_ID=
VITE_FIREBASE_STORAGE_BUCKET=
VITE_FIREBASE_MESSAGING_SENDER_ID=
VITE_FIREBASE_APP_ID=
VITE_SENTRY_DSN=

3. Backend environment variables

Create functions/.env:

GOOGLE_CLIENT_ID=
GOOGLE_CLIENT_SECRET=
RESEND_API_KEY=
REMINDER_FROM_EMAIL=you@yourdomain.com
SENTRY_DSN=

4. Install frontend dependencies

npm install

5. Set up the Python virtual environment

macOS / Linux:

cd functions
python3.11 -m venv venv
source venv/bin/activate
pip install -r requirements.txt
cd ..

Windows:

cd functions
python -m venv venv
venv\Scripts\pip install -r requirements.txt
cd ..

6. Connect the Firebase project

firebase use --add

Select your Firebase project from the list.

7. Run locally

npm run dev

8. Deploy to production

firebase deploy --only hosting,functions,firestore
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