Startup Ideas: How do you know if your startup idea already exists?

The better question is "Did my startup idea already exist and fail?"

To find out, talk to as many potential customers as you can, describe your idea, and ask them if they have ever seen such a similar product or service?

If they say yes, ask them if they used it.  If they did, find out why they stopped.

If they say no, ask them if they would buy such a product and how would they make it better

Now you are going to say, 'I can't run around telling people about my great idea. Someone will steal it.'

Don't worry. As many others have pointed out; ideas are easy, execution is hard. If someone else can become more excited, passionate, and driven about your idea after a one conversation; you shouldn't start the business.

If they truly do get excited and passionate about your idea, have them be an angel investor, or one of your first customers, or maybe even a co-founder.