There is indeed a need to have access to a decent SEO api that is going to provide you with SEO data which you could use when ranking websites on search engines. You have quite a few options available when looking for tools that will allow you to get details about keywords as well as about competition that you are looking to outrank for a decent spot on the first page of Google for specific search queries.
Many would think purchasing every single tool out there would be the best way to go however it is indeed not an efficient way of getting things done. The reason being, you will find it tough to work with several tools for a single project which is why many SEO experts are nowadays after those tools that they can use for multiple purposes as opposed to a single purpose for that matter.
You may therefore find going for an seo api to be the best solution as you can be getting data that you need for a small fee that you pay towards your subscription. With an SEO API, you could be getting the value of any keyword that you come across together with getting all relevant information on what it takes to rank for it on the first page under a single subscription.