CalPal

A fast, self-hosted, and lightweight scheduling alternative with zero external dependencies.

CalPal is a streamlined, compiled scheduling application designed to be a drop-in replacement for tools like Calendly. Built with Go and SQLite, it requires no heavy external databases and deploys instantly via a single lightweight Docker container.

Features

• Zero-Dependency Deployment: Powered by a pure-Go SQLite driver (modernc.org/sqlite).
• Timezone Resilience: Built-in timezone database resolution ensuring flawless scheduling across the globe.
• Native Calendar Invites: Generates strict, RFC 5545 compliant .ics attachments and multipart MIME emails for native RSVP support in Gmail and Outlook.
• OAuth Integrations: Connects directly with Google and Microsoft Calendars.

Screenshots

Environment Variables

CalPal is configured entirely through environment variables, making it highly compatible with Docker, Kubernetes, and minimal cloud environments.

Variable	Description	Default	Example
PORT	The port the web server will listen on.	8080	8080
BASE_URL	The fully qualified URL of your deployment (used for callbacks and links).	http://localhost:8080	https://cal.yourdomain.com
SMTP_HOST	The hostname of your SMTP provider for transactional emails.	(None)	smtp.mailgun.org
SMTP_PORT	The port for your SMTP provider.	(None)	587
SMTP_USER	Your SMTP username.	(None)	postmaster@yourdomain.com
SMTP_PASS	Your SMTP password.	(None)	super-secret-password
SMTP_FROM	The email address notifications will be sent from.	(None)	bookings@yourdomain.com
GOOGLE_CLIENT_ID	OAuth Client ID for Google integration.	(None)	12345-abcde.apps.googleusercontent.com
GOOGLE_CLIENT_SECRET	OAuth Client Secret for Google integration.	(None)	GOCSPX-abcdefghijklmno
MICROSOFT_CLIENT_ID	OAuth Client ID for Microsoft integration.	(None)	abcd-1234-efgh-5678
MICROSOFT_CLIENT_SECRET	OAuth Client Secret for Microsoft integration.	(None)	secret-value-here
MICROSOFT_TENANT_ID	OAuth Tenant ID for Microsoft. Use common for personal accounts.	common	1234abcd-56ef-78gh

Running with Docker

CalPal is distributed as a highly optimized, multi-stage Docker container.

1. Build the image:

   docker build -t calpal-app .

2. Run the container: Ensure you map a volume for your SQLite database (calpal.db) so your data persists across restarts.

   # Create an empty database file first so Docker maps it as a file, not a directory
   touch calpal.db
   
   docker run -d \
     -p 8080:8080 \
     -v $(pwd)/calpal.db:/app/calpal.db \
     -v $(pwd)/templates/email_template.html:/app/templates/email_template.html \
     -e BASE_URL="[https://cal.yourdomain.com](https://cal.yourdomain.com)" \
     -e SMTP_HOST="smtp.provider.com" \
     -e SMTP_PORT="587" \
     --name calpal \
     calpal-app

OAuth Integration Guide

To allow CalPal to sync automatically with host calendars, you need to configure OAuth credentials with Google and/or Microsoft.

Google Calendar Setup

1. Go to the Google Cloud Console.
2. Create a new project (e.g., "CalPal Scheduling").
3. Navigate to APIs & Services > OAuth consent screen and configure it for "External" use.
4. Navigate to APIs & Services > Credentials.
5. Click Create Credentials > OAuth client ID.
6. Select Web application as the application type.
7. Under Authorized redirect URIs, add your base URL followed by the Google callback path:
   • Example: https://cal.yourdomain.com/auth/google/callback
8. Click Create. Copy the resulting Client ID and Client Secret into your GOOGLE_CLIENT_ID and GOOGLE_CLIENT_SECRET environment variables.
9. Note: Ensure you have enabled the "Google Calendar API" in the library for this project.

Microsoft Outlook Setup

1. Go to the Azure Portal.
2. Navigate to Microsoft Entra ID (formerly Azure Active Directory) > App registrations.
3. Click New registration.
4. Name your app (e.g., "CalPal") and select "Accounts in any organizational directory and personal Microsoft accounts".
5. Under Redirect URI, select Web and input your base URL followed by the Microsoft callback path:
   • Example: https://cal.yourdomain.com/auth/microsoft/callback
6. Click Register. The "Application (client) ID" shown is your MICROSOFT_CLIENT_ID. The "Directory (tenant) ID" is your MICROSOFT_TENANT_ID (or use common if you selected personal accounts in step 4).
7. Navigate to Certificates & secrets in the left menu.
8. Click New client secret, give it a description, and click Add.
9. Copy the Value of the secret (not the Secret ID) and use it as your MICROSOFT_CLIENT_SECRET environment variable.