Snapchat is building a platform with a plug-in tool for brands and agencies to automate advertising purchases on its app, according to a source for Digiday.

The so-called application program interface, or API, would give Snapchat’s customers the ability to purchase digital advertisements on the company’s app using ad-buying software. Snapchat now sells advertising by hand, but to better compete with social media rivals Facebook and Twitter, the company will need to automate more of its advertising sales process.

Though Snapchat Chief Executive Evan Spiegel was initially wary of some digital advertising technology, for example calling user-targeting technology “creepy,” gradually the company has been adding capabilities. In September, Snapchat started selling “audience bundles,” advertising packages thematically grouped around the app’s Discover Channels.

An API that allowed agencies and brands to automatically buy advertising from Snapchat would substantially increase the number of advertisements the company could sell. Increasing revenue is must for Snapchat, which is seeking to justify a reported $16 billion private valuation before following through on its plan to make an initial public offering of its stock in the next several years.

Technology reporter Garrett Reim can be reached at greim@labusinessjournal.com. Follow him on Twitter @garrettreim for the latest in L.A. tech news.