How they supposedly work: These tools often rely on scraping publicly accessible member lists from very large public groups and compiling them into databases. If a user is a member of many public groups, and these groups were crawled, their username/ID might appear in such a database.
Major Limitations and Risks (Crucial News):
Only Public Groups: These tools cannot access private groups. If a user is primarily in private groups, they won't be found this way.
Outdated Data: Such databases are constantly outdated as users join and leave groups, and Whatsapp frequently updates its anti-scraping measures.
Ethical & Legal Issues: The creation and use of such databases for non-investigative purposes often raise significant ethical and legal concerns regarding data privacy.
Malware Risk: Any unofficial "group scanner" bot you find online is a major security risk. Recent news (April-May 2025) has highlighted severe cybersecurity threats, including "rogue npm uk whatsapp number data packages" that mimic Whatsapp Bot APIs to plant backdoors and steal credentials. Never use unverified third-party bots or tools.
Whatsapp 's Crackdown: Whatsapp actively works to prevent large-scale data scraping and the misuse of its platform. Features like the removal of "People Nearby" (September 2024) demonstrate their commitment to user privacy against such exploitation.
Contact Confirmation (New in March 2025 Update):
News: Whatsapp 's March 2025 update introduced a "Contact Confirmation" feature. When an unknown user sends you a message for the first time, Whatsapp will now display an info page with details like:
The sender's country (based on their phone number).
Account history (join date, recent profile changes).
Indicators for official/verified accounts.
What this means: This is a security feature for you, to help you spot scams. It confirms if you share groups with an unknown sender, but it doesn't let you browse their entire list of groups. It only shows mutual groups in that specific context.
In Summary:
Default Behavior: You can only see groups you share with another user on Whatsapp . This is by design for privacy.
No Official Feature: Whatsapp does not provide a feature to see all groups someone is a member of.