You need feedback from the people you think would be interested in it. To get that you have several options:
1) Ask friends/family in your theorized target persona if they'd be interested.
2) Post on online communities asking the same thing (e.g. appropriate sub-Reddits).
3) Go in person to the workplaces of your target persona. Bring donuts, or coffee or something around lunchtime, introduce yourself and ask nicely and casually if you could ask them some questions (i.e. if they would be interested in xyz, why/why not, any suggestions, etc.)
4) Make a quick 'landing page' on Weebly or Squarespace, and then do cheap advertising on Google, Facebook, etc. to draw people to it. Make sure you set up analytics first (e.g. Google Analytics)
5) Be creative and think of some other way
If you'd like more specific advice tailored to your actual idea I'd be happy to help out,