So you want to put an API in place to access your schema-less database? So that multiple applications can access your database in a consistent manner? That makes sense.
You know what though... you may want to use multiple programming languages, and maintaining an API in multiple languages sucks. So, why not just make a service that each application can connect to, and then let it talk to your database. Then you just need to define a simple protocol that language can use to connect to your service.
Or, you could just skip a few steps and use an actual database to begin with.
Building an API is still a great choice no matter how good your database is. Why would you not have an API if you are using the data store from 5 difference languages?
You know what though... you may want to use multiple programming languages, and maintaining an API in multiple languages sucks. So, why not just make a service that each application can connect to, and then let it talk to your database. Then you just need to define a simple protocol that language can use to connect to your service.
Or, you could just skip a few steps and use an actual database to begin with.