As a developer and web designer, it’s important to know as many platforms as possible. With that being said, it’s important to know the difference between all interfaces and platforms as well. Here is the difference between an API & an SDK:
API (Application Programming Interface)
For example, Amazon.com released its API so that Web site developers could more easily access Amazon’s product information. Using the Amazon API, a third party Web site can post direct links to Amazon products with updated prices and an option to “buy now.”
An API is a software-to-software interface, not a user interface. With APIs, applications talk to each other without any user knowledge or intervention. When you buy movie tickets online and enter your credit card information, the movie ticket Web site uses an API to send your credit card information to a remote application that verifies whether your information is correct. Once payment is confirmed, the remote application sends a response back to the movie ticket Web site saying it’s OK to issue the tickets.
Providers of SDKs for specific systems or subsystems may sometimes substitute a more specific term instead of software. For instance, both Microsoft and Apple provide driver development kits (DDK) for developing device drivers.