Design a calendar API like Google Calendar
PremiumAPI designHard
- RRULE recurrence
- IANA time zones
- Recurring event exceptions
Quick answer
This API design interview question asks you to design a calendar API like Google Calendar. Aim for a design that exposes a clear, consistent and safe interface, then explain the resources, requests, responses and error handling. Interviewers want to see how you name resources, version the interface and handle failure cases.
The problem
Design a calendar API like Google Calendar for a workplace suite's apps and third-party scheduling tools. The hard parts are recurring events with one-off exceptions, time zones (a 9:00 London meeting stays at 9:00 London time when the clocks change), free/busy lookups and safe concurrent edits.
Users create one-off and recurring meetings, invite people across countries and change one occurrence of a weekly meeting. Design the public API for calendars, events, recurrence, attendees, availability and sync.
What must a calendar API like Google Calendar do?
- Recurrence: Daily, weekly, monthly and yearly rules with interval, by-day, count or until (RFC 5545 RRULE).
- Time zones: Every timed event has an IANA zone; clients can view in any zone.
How well must it do it?
- Correctness: Occurrences stay at the same local wall-clock time across DST changes.
- Concurrency: Two people editing the same event never silently overwrite each other.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- RRULE recurrence
- IANA time zones
- Recurring event exceptions
- Free busy queries
- Etag concurrency
- Sync tokens
How you’ll practise
- Use cases
- Resources
- Endpoints
- Errors, auth and limits
- Versioning
- Wrap-up
Lala, personalized to you, gives a hint when you ask and reviews your design when you are ready.
What do interviewers look for?
In any API design round.
- Starts from the clients and the use cases
- Names resources and operations consistently
- Defines request and response shapes and status codes
- Covers authentication, rate limits and idempotency
- Plans pagination, filtering and versioning
- Explains how clients learn about and recover from errors
Questions people ask about this interview question
- Which design type is this question?
- It is an API design question. You design a calendar API like Google Calendar and explain your choices the way you would in an interview.
- Is this question asked at entry level?
- It is marked Hard. It suits engineers preparing for senior interviews, where you are expected to drive the discussion and go deep on trade-offs.
- What should I cover first?
- Start with the clients, the main use cases and the resources they need. Agree on scope with the interviewer before you design anything.
- Can I practise it for free?
- It is a premium question. Sign up and unlock it once for 10 credits; it then stays unlocked. When you finish, Lala, your personalized AI mentor, can review your design for 30 credits.
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Updated · Written by the SevyDevy team