An ad API (application programming interface) program is usually offered by a PPC ad platform to advertisers, agencies and software / service vendors. By using an API program these different partners can develop build custom tools which enables advertisers and agencies to have more control over their ad campaigns and to automate some operations without passing through the classic self-service interface used by most clients.
Through APIs, dedicated applications may automatically create thousands of ad variations or set rules that reallocate ad spend in real time.
PPC Bid management softwares which enable advertisers to centralize their bids and announces delivered to several PPC search engines are using API programs.
All large PPC search engines and social media platforms have their own API platform. Usually API programs are only accessible for approved companies. Some companies charge users for API calls and others don’t.
API programs might also emerge for display advertising.
See also Adwords API.
Some ad API examples: