The Mechanics of WhatsApp Contact Sync
WhatsApp relies on your phone's address book to connect you with friends. It continuously scans your contact list for phone numbers that are registered on WhatsApp.
How the Process Works
- Permission Grant: When you first install WhatsApp, you grant it permission to read your contacts.
- Hashing & Upload: WhatsApp hashes the phone numbers in your address book and sends them to its server.
- Matching: The server checks which hashed numbers match existing user accounts.
- Display: Matched contacts appear in your WhatsApp list instantly.
Troubleshooting Sync Issues
If your contacts aren't showing up:
- Go to your phone Settings > Apps > WhatsApp > Permissions and ensure "Contacts" is allowed.
- Open WhatsApp, go to Select Contact (New Chat) > Options (three dots) > Refresh.