Cal Henderson

Co-founder and Chief Technology Officer, Slack

Cal Henderson oversees the engineering organization at Slack. He is an experienced technology leader, having previously built and led the engineering team at Flickr, through its acquisition by Yahoo.

In 2019 he was recognized as a Young Global Leader by the World Economic Forum and was included in Fortune magazine's "40 under 40" list.

As a popular speaker on engineering scalability, he authored the best-selling O’Reilly Media book Building Scalable Websites. He was a pioneer in the use of web APIs, and created the basis for OAuth and oEmbed, now used by YouTube, Twitter, and many others.

Cal has a BCS from the University of Central England, and was involved in London’s early online community through his work with the early digital community B3ta and his personal blog, which he has run for over 20 years. Cal now resides in San Francisco.

About has been online for 23 years, 341 days, 15 hours, 53 minutes and 7 seconds - crumbs! is primarily cal henderson's personal site, containing his linklog/weblog which he's been posting to regularly since June 2000:

It also hosts a discussion forum where anyone can signup and post. The topic is roughly "whatever". more »

An incomplete list of other sites that Cal has created or been involved with can be found on the network homepage.


Please do not contact me at my personal address regarding Slack. Instead, use for press or speaking enquiries, or for any other issues.