From Wikipedia: “An application programming interface (API) is a particular set of rules and specifications that a software program can follow to access and make use of the services and resources provided by another particular software program that implements that API.” In other words API is a kind of protocol which a software developer can use to create software that works with a particular service (API provider).
Betfair has it’s own API to allow software developing companies make software which access Betfair’s data. In this case Betfair is service provider and other companies are clients to it’s services. The API can be used in different programming languages which support web services. It can be utulised even in Excel.
The API has been designed for two purposes. First is to give vendors a unified, not html-dependent way to make Betfair software. Second is to control increasing number of software and minimize security risks for users who use the software. The second purpose is achieved by requirement to pass certification process to access API for every redistributable software.
There are Free API (personal) and Vendor API (commercial). Commercial API is dedicated for software vendors who want to distribute their software to other users. Usually it’s a trading software or software for tipsters. It’s goals are speed and manageability. You have a vendor control panel where it’s possible to manage Betfair users who can use your software. However Vendor API costs 200 GBP per month to a vendor. Free API doesn’t have any charges, but the number of requests is limited. For instance, it’s not allowed to request market prices more than 60 times per minute. Here is the official Betfair page comparing these two APIs.
Free API can be easily accessed by anyone who has some programming knowledge. There are free samples which demonstrate how to utilise the Betfair API.