Ask HN: What's the best way to guage interest in a product idea?

I have an idea for a SaaS startup that could potentially make money. I'm just wondering, what's the best way to guage if companies are actually interested in this product without giving away the idea to publicly?

The idea is not entirely new - there are a few players, but no one really big. And I kind of have a USP with this idea.

So I could potentially ask publicly, but is it worth the risk?