Send a survey to 100+ of your active users and ask the following questions:
1. How would you feel if you could no longer use the product?
→ If the “Very disappointed” percentage is over 40%, you are on track to PMF.
2. Compared to other ways you do [essential function of your product], using this product to do it is generally:
→ Look for signs that your product is moving in a positive direction.
3. The last time you did X, what product or tool did you use to do it, and why? [Open-ended]
→ Since this is a behavioral question, it will give you an idea of whether your product is being used in the context and times you think it should be.