CalDAV (RFC 4791) is an extension of WebDAV that provides a standard protocol for accessing and managing calendar data on a remote server. It enables shared scheduling and synchronization across clients.
CalDAV
CalDAV, standardized as RFC 4791, is an extension of WebDAV that defines how clients read, write, and synchronize calendar data stored on a remote server. It models calendars as WebDAV collections of iCalendar (.ics) resources and adds calendar-aware operations—most importantly a reporting mechanism for querying events by time range and properties. The result is one interoperable protocol that lets many different clients share the same calendar.
- Built on WebDAV and HTTP - Reuses the existing verbs, authentication, and resource model of the web rather than inventing a new transport.
- iCalendar payloads - Calendar objects are carried as standard iCalendar data, so events, to-dos, and free/busy time are portable across systems.
- Calendar queries and scheduling - The
calendar-queryreport and scheduling extensions support time-range filters, invitations, and free/busy lookups. - Multi-client synchronization - The same server-side calendar can be kept in sync across phones, desktops, and web apps at once.
CalDAV is the quiet standard behind cross-vendor calendaring—the reason an iCloud, Google, or Fastmail calendar can be read and updated by a third-party client without a proprietary API. For anyone integrating scheduling, it shows up as a mature, HTTP-native alternative to a bespoke REST calendar API, and it sits alongside its contact-focused sibling CardDAV as part of the WebDAV family. In an agentic world, that standardized, queryable surface is exactly what lets an assistant negotiate free/busy time and book events across providers.
