Discover APIs from all over the web and beyond. API For That is an API directory. Don’t waste time building things that somebody else has already built. In most cases, if there’s a service you can rely on, you should use it. It will speed up your development, so you can focus on your core competence?—?which is your real IP. If a third-party service seems expensive at first, do the math and compare the costs?—?both monetary and opportunity?—?of building and maintaining it in-house.