Connecting Blocks: While building with Lego blocks, which parts, and how many of them connect together is obvious. Similarly, an API should connect well with developer applications and other APIs provided by other API providers. Industry standards like OAuth and REST etc., help in solving this connectivity problem. It is easy to see whether a LEGO block is connected well or not. Similarly, an API should have efficient error and exception management features.
Easy to Build: At the end of your play with the LEGO blocks, you realize that you have built stuff without getting your hands dirty. Similarly, APIs should not damage a developer’s code or make him compromise it. They should help him easily integrate his code with the platform to encourage evolution of products.
Open-Ended Nature: LEGO blocks are components, designed to build multiple and varied structures, and as far as building things from them is concerned, your imagination is the limit. They empower and inspire the imagination of users, to CREATE. In the same spirit, APIs should challenge a developer’s imagination. The API providers themselves benefit from an open-ended API, as it lets developers use it in collaboration with other APIs to create compelling products. This integration and usage of multiple APIs to create new products is known as a Mashup. While APIs solve the core problem of making their service or product accessible, Mashups do the rest.
Tool Free: You don’t need any tools to build a structure with Lego blocks; just your hands are enough. Similarly a good API shouldn’t require any tool to be used within the application. This means, the core API should work without the development of a dedicated SDK.