How to verify the product is market fit before its launch?

A survey in social networks. Website for the prototype before the start of development

Beta testing and requesting feedback from the early users :)

Launch a direct marketing campaign landing them to a prototype website or a webinar registration page. Then collect feedback through a survey or an interview.

Make a survey, ask people in FB groups

Well whatever you are doing you should be showing users something. Superhuman has an excellent framework for their path to PMF: https://review.firstround.com/ho...

You don't ... not for sure. The standard solution to this is to *launch* an MVP, and use that to *estimate* viability.

Yeah I've read from YC that you likely have achieved PM fit if growth is NOT your problem but keeping up with demand is