Introduction

CalendarAPI was originally built to power an e-Paper-based meeting room display, running on an ESP32 Since the device had limited memory and parsing iCal calendars in Arduino C would’ve been a major hassle, CalendarAPI offloaded that complexity into a dedicated Go service that exposes the parsed calendar data over both REST and gRPC APIs.

While it started as a backend utility, CalendarAPI quickly proved useful beyond its original scope. It became a handy CLI tool to check daily calendar events via calendarapi get calendar, and even got a HomeAssistant Add-On for seamless integration into smart home setups. With RESTful sensors and RESTful commands, it can power HomeAssistant sensors or display contextual info on the e-Paper device.

CalendarAPI also supports custom status messages per calendar, making it easy to show tailored messages on displays throughout the day—whether it’s “In a meeting” or “Out for lunch.”

At its core, CalendarAPI exists to make calendar data more accessible, automatable, and adaptable to embedded devices and home automation systems.