History of APIs - del.icio.us
del.icio.us is a social bookmarking service for storing, sharing and discovering web bookmarks to web pages, that was founded by Jousha Schachter in 2003.
Del.icio.us implemented a very simple tagging system which allowed users to easily tag their web bookmarks in a meaningful way, but also established a kind of folksonomy across all users of the platform. Which proved to be a pretty powerful way for cataloging and sharing web links.
The innovative tagging methodology used by del.icio.us allowed you to pull a list of your tags, or public web bookmarks by using the URL http://del.icio.us/tag/[tag name]/. So if I was searching for bookmarks on airplanes, I could http://del.icio.us/tag/airplane and I would GET a list of all bookmarks that have been tagged airplane. It was simple
When it came to the programmatic del.icio.us interface, the API was built into the site, creating a seamless experience--if you wanted the airplane tags via HTML you entered http://del.icio.us/tag/airplane, if you wanted RSS of the tags you entered http://del.icio.us/rss/tag/airplane, and if you wanted XML returned you used http://del.icio.us/api/tag/airplane. This has changed with the modern version of Delicious API.
del.icio.us was the first, concrete example of how the web could deliver HTML content, alongside machine readable like RSS and XML, using a URL structure that was simple and human readable. This approach to sharing bookmarks would set the stage for future APIs, in making APIs easy to understand for developers and even non-developers alike. Any slightly technical user could easily parse the XML or RSS, and develop or reverse engineer widgets and apps around del.icio.us content.
del.icio.us has been sold twice since its early popularity, which included to Yahoo! in 2005 and AVOS Systems on April, 2011. However del.icio.us was one of the pillar platforms that ushered in the social era of the API movement, establishing sharing via APIs as critical to the API economy, but also showing that simple rules when it comes to API design.