このガイドの全文は現在、英語のみで提供されています。
The short answer
In most jurisdictions, looking at information a stranger has published under a public handle is not itself unlawful. You are reading the same pages anyone could open in a browser.
What is regulated is rarely the viewing. It is what you do next: how you store the data, whether you contact the person, whether you publish what you found, and whether your purpose is legitimate.
Public data, not private access
The line every legitimate tool stays on is that it never authenticates as anyone. It does not log in, does not use anyone else's session, and does not defeat a privacy setting. If a profile is private, a scan at most confirms the account exists.
Anything that does cross that line — credential sharing, scraping behind a login, buying breached data — moves the activity into a completely different legal category, regardless of how good the intention was.
Where it crosses a line
Searching becomes harassment when it turns into a pattern of unwanted contact, or when its purpose is to intimidate. It becomes doxxing when you publish identifying details that were not already public in a way that exposes someone to harm. Those are the risks that carry real consequences.
There is also data-protection law to consider if you keep the results: in the EU and UK, personal data you store about someone can fall under GDPR regardless of how you obtained it, which brings rules about purpose, retention and the person's right of access.
If you are the one being searched
You are allowed to look for yourself, and it is worth doing. Search your own handles, see what a stranger would see, and decide platform by platform whether that is acceptable.
If someone else's searching crosses into harassment or publication, the practical steps are to document what happened with timestamps, report it to the platform, and in serious cases take legal advice rather than retaliating online.