“Step three — reach out to those users with your solution, with just a basic landing page explaining your solution. So messaging is the key here.”

Reach out to the competitor's users with a landing page before writing any code

After identifying a popular tool and the unmet pain points around it, validate demand by DM'ing those users with a basic landing page describing the solution. No product is required yet — messaging is what determines whether they bite, and that proves intent before any code gets written.