CardDAV (RFC 6352) is an extension of WebDAV that defines a standard protocol for accessing and sharing contact information on a remote server. It enables address-book synchronization across devices and applications.
CardDAV
CardDAV, standardized as RFC 6352, is an extension of WebDAV that defines how clients read, write, and synchronize contact data stored on a remote server. It models an address book as a WebDAV collection of vCard resources and adds contact-aware queries, so different clients can share one canonical set of contacts. It is the address-book counterpart to CalDAV’s calendars.
- Built on WebDAV and HTTP - Reuses the web’s existing verbs, authentication, and resource model rather than inventing a new transport.
- vCard payloads - Contacts are carried as standard vCard data, keeping names, addresses, phones, and emails portable across systems.
- Address-book queries - The
addressbook-queryreport filters contacts by property, so clients fetch only what they need. - Multi-client synchronization - The same server-side address book stays in sync across phones, desktops, and web apps.
CardDAV is the standard that lets a contacts list live on a server and be edited from many clients without a proprietary API—the reason an iCloud, Google, or Fastmail address book opens cleanly in third-party apps. For anyone integrating contact management, it is a mature, HTTP-native alternative to a bespoke REST contacts API, and it pairs directly with its scheduling sibling CalDAV in the WebDAV family. That standardized, queryable surface is also what makes a contact store legible to an agent acting on a user’s behalf.
