CardDAV is the standard that many address book servers use, such as Fastmail, Zoho Mail and Nextcloud. It does not find duplicate contacts. It does not merge them either.
Nextcloud has a button to merge 2 contacts by hand. Below are its steps, starting with a backup.
How CardDAV handles duplicate contacts
CardDAV is an open standard for keeping address books on a server.
What the standard does:
- It stores and reads your contacts. It has no way to find duplicates and no merge.
- It allows two contacts for the same person in one address book.
What the apps do:
- Apple Contacts has a merge for duplicate cards. It works on cards in one account.
- DAVx5 syncs your CardDAV address books to your Android phone. It has no duplicate tool that we found.
- Nextcloud Contacts can merge two contacts by hand. The steps are below.
How to remove duplicate contacts in Nextcloud
Export a backup first. In Nextcloud Contacts, open Contacts settings at the bottom left. That is where Nextcloud lets you export an address book. Keep the file until you are done.
These are Nextcloud's steps for the Contacts app. Nextcloud does not say it finds duplicates for you. If you do not see Contacts, install it from the Nextcloud App Store.
- Select the two contacts.
- Click the Merge contacts button at the top of the contacts list.
- Nextcloud shows both contacts side by side.
- For each detail, choose the value to keep. Some details take one value, such as the name. Others let you keep several, such as phone numbers and emails.
- The merged contact joins every group that either contact was in. Clear any group you do not want.
You can merge only two contacts at a time. You can merge only contacts you are allowed to change.
Nextcloud's "Recently contacted" address book. In some versions it stored a duplicate when you emailed someone already in your address book. Nextcloud fixed that case in 2023. Another case is still open: a user contacted by a share and by a calendar invite can be stored twice. You can switch the app off in Nextcloud.
Where CardDAV stops
No standard merge. Nothing in CardDAV says two contacts are the same person. Each app has its own tool, or none.
One address book at a time. A CardDAV address book knows nothing about the same person in Google or Outlook. The duplicate stays. To see how that works across accounts, read how to merge contacts across accounts.
Manual work. Nextcloud merges two contacts at a time. A long list of duplicates takes a long time.
Merge a whole group at once with ContactZapp
Take Anna Nowak. Nextcloud has her twice, with her work email and phone number. Google has her as "A. Nowak", with her personal email and the same phone number. In Nextcloud you merge the 2 copies. Google still has the third.
ContactZapp finds duplicates within one account and across accounts. It shows all 3 contacts as one group, side by side, and suggests the values to keep. You review the group once. The merged contact keeps both email addresses. It is sent to Nextcloud and Google. You can undo the merge for 12 months.
See how merging across accounts works.
FAQ
Does CardDAV remove duplicate contacts? No. CardDAV stores your contacts and has no merge. Whether you can remove duplicates depends on your server or app.
Can Nextcloud merge duplicate contacts? Yes. The Nextcloud Contacts app has a Merge contacts button. It merges two contacts at a time, and you choose which values to keep. Nextcloud does not say it finds duplicates for you.
Can Nextcloud merge more than 2 contacts at once? No. Nextcloud merges 2 contacts at a time. If a person has 3 copies, merge 2 of them. Then merge the result with the third.
Why does Nextcloud add duplicate contacts? The "Recently contacted" address book can store a second copy of someone you already have. Nextcloud fixed the email case in 2023. You can switch the app off.
Which CardDAV servers does ContactZapp work with? CardDAV servers such as Fastmail, Zoho Mail and Nextcloud. Fastmail has no CardDAV on its Basic plan. ContactZapp connects one address book per account.