Cal Henderson

Technology executive

Cal Henderson was the co-founder and CTO of Slack for 15 years, from inception through to public listing on the NYSE and finally its 2021 acquisition by Salesforce for $27.7 billion. In this role he oversaw Slack’s world-class engineering, research and design teams and set the technical vision for the company.

He is an experienced technology industry leader, having previously built and led the engineering organization at Flickr, from founding through to its acquisition in 2005 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.

Cal is currently focused on advising and investing in the next generation of great software leaders.

As a popular speaker on engineering scalability, he authored the best-selling 2006 O’Reilly Media book Building Scalable Websites. He was a pioneer in the use of web APIs, and co-created many foundational web technologies including OAuth and oEmbed.

Cal has a BSc from the Birmingham City University in 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 with his wife and children.

About has been online for 24 years, 66 days, 1 hour, 10 minutes and 48 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.