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I'm Slack CTO Cal Henderson, and This Is How I Work
how i work

I'm Slack CTO Cal Henderson, and This Is How I Work

Nick Douglas, Gawker Media

Cal Henderson is the co-founder and CTO of Slack, the leading workplace messaging platform, which Henderson's team invented while trying to build an online game called Glitch. That wasn't the first time Henderson and his Slack co-founder Stewart Butterfield set out to build a game and ended up with a startup. In the early 2000s, Henderson joined Butterfield's team to build Game Neverending, which spawned the photo-sharing site Flickr. He's been programming (and blogging at iamcal.com ) for 15 years.

We talked to Henderson about how he works, how he Slacks, and how it feels to pivot into massive success-twice.


Location: San Francisco
Current Gig: CTO of Slack
One word that best describes how you work: Relentless
Current mobile device: iPhone 7 with the ugly battery case
Current computer: 11" MacBook Air, but running Windows

Tell me a little about your background and how you got to where you are today.

I got into computers at a pretty young age; it started when my older cousin got a Texas Instruments TI-99 when I was around six. Like most computers at the time, it came with a BASIC interpreter, and I was fascinated. Within a few years I had decided that programming is what I wanted to do when I grew up. I've been pretty obsessed ever since.

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I've been in San Francisco for 12 years now, initially coming to San Francisco from Vancouver with the acquisition of Flickr by Yahoo. During my time at Flickr, I spearheaded a number of technologies that are still commonly used, including APIs, oAuth, and oEmbed, and wrote a best-selling O'Reilly book, Building Scalable Web Sites . I worked on Flickr at Yahoo for 4 years before leaving in 2009 to start an MMO [massively multiplayer online game] called Glitch with Stewart Butterfield, Eric Costello and Serguei Mourachov, all from Flickr.

What's your workspace setup like?

I have a desk in our headquarters, but I'm rarely found there. Most of my days are spent in meetings. Given our SF HQ office is 50,000 sq ft, I'm able to get most of my 15,000 daily steps during work hours.

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However, when I am found at my desk, you'll notice that my desk is usually a mountain of junk. I use a very small laptop (11" MacBook Air, RIP) but plug into external monitors whenever I can. I'm also a mechanical keyboard nerd, and currently use a tenkeyless Varmilo with blue Cherry MX switches. It's super loud and sounds a bit like a typewriter.

What's your best time-saving shortcut or life hack?

Listening to audiobooks at 2-3x speed. I switched almost exclusively to audio books about 5 years ago, so I could combine my walking commute with reading, but finding the speed setting has been a real boost.

How do you recharge? What do you do when you want to forget about work?

Listening to books or podcasts at 3x speed while playing iPhone games; Bit City is the latest one to catch on in the office. Or, spend time with my 3-year-old son. Nothing forces you to reorient your attention like a toddler.

What's your sleep routine like?

I have a very regular sleep schedule: I'm typically in bed by 10:30 and asleep by 11:30. I usually spend 30-60 mins at the end of the day winding down, listening to sci-fi books. I wake up at 7:30am every day.

You and your co-workers famously developed Flickr and Slack while developing video games. What were these pivots like? What was different the second time around, Slack vs. Flickr?

The pivots were hard-no one sets out to fail. You don't know, when you're going through shutting down a failed company, that there will be a good outcome on the other side.

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What's been different this time around is the growth and maturity of the web as a platform-there are 100x more people online everyday. When we built Flickr, the idea of putting your photos online was pretty new. Now the idea of putting them anywhere else is weird.

The other big shift is the development of infrastructure and the cloud. The bar to getting started has gotten lower and lower, allowing you to spend less time racking servers and more time working on the thing you're trying to build.

What everyday thing are you better at than everyone else? What's your secret?

That's a bit full-on. I've been told I have a tremendous capacity for focused work and high-output, but what's allowed me to grow into the CTO role at an org the size of Slack has been my 15-year history of managing teams and the reward I find in the human aspects of the work. There's a very prevalent stereotype that engineers are socially unsophisticated, but that's just not the case. Interpersonal communication is an absolute requirement for management and leadership in all functions of a company, and no less so in engineering. It's a team activity.

What apps, software, or tools can't you live without?

  • Work: Slack
  • News: BBC, Twitter
  • Family: Whatsapp, Snapchat
  • Entertainment: Audible, Reddit

What's your biggest struggle in the workplace?

Probably prioritizing my time. As an organization grows in size and complexity, it's easy to fall into just being reactive. There's always one more thing coming to you that wants attention and needs to be done now. But stepping back and being strategic about what you focus on is really important.

What do you listen to while you work?

I spend most of my workday in meetings, but when I'm working from home I'll plug into Spotify-this week has been a mix of Kanye and (British trip-hop group) Sneaker Pimps .

What are you currently reading, or what would you recommend?

I recently finished Ada Palmer's Terra Ignota series , which I strongly recommend. A view of humanity post-scarcity and what it takes to hold a society together.

What's the best advice you ever received?

I'm not sure where this advice came from, but the idea of finding a set of people you like to work with, rather than the perfect project. We didn't set out to make Flickr, or start a company to make Slack, but finding a group of people that you trust and love to work with means that you enjoy what you're doing, even when you pivot into something completely different.

And to drink lots of water and get regular exercise.

What's the greatest idea you've had that you don't want to do yourself?

I still think that what we were trying to do with Glitch (a multiplayer online social game space around would building and collaboration) is a great idea. We didn't manage to make it into a successful business and I don't think I'll try doing it again, but the core of the idea was great. If someone manages to make what we were aiming to, I'd play the shit out of it.

What's your own Slack etiquette, and how much does it line up with the rest of your team? For example, how much do you use Slack during off-hours? Have you ever made a big faux pas like sending a sensitive message to the wrong channel?

I think I make that mistake more often with email than with Slack, probably because I use it less frequently. While I read Slack at all hours, I try to avoid DMing people late at night. The pressure for people to respond quickly can guilt people into thinking they need to be always on. Queuing up a bunch of messages to send first thing in the morning lets people know that my questions can wait.

You've pulled off some great stunts, like the "who looks like a manager" game at Yahoo. [Henderson's game asked fellow Yahoo employees to guess which of two people was higher up at the company, based only on their photos.] What role have side projects played in your career?  

I had a lot of fun with the early internal Hack Days at Yahoo, showing that you could build interesting projects that weren't just a user-facing product feature.

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Playing Game Never Ending (the game that preceded Flickr) was something I did for fun in my spare time in my early 20s, but 'hacking' into the system to understand more about how the game worked is what ultimately led to being recruited by Stewart to come work at Flickr.

Fill in the blank: I'd love to see _________ answer these same questions.

Jay Parikh (VP of Engineering at Facebook)

Is there anything else you'd like to add that might be interesting to readers and fans?

I've always loved the way you can use software to just make stuff, and get it into the hands of people quickly. If that's something that you enjoy, right now is a great time to get into the industry. There's a lot of opportunities to make things that people use and rely on every day. As an industry we still have a long way to go, but there's never been a better time to pursue a career in software engineering; you don't need to have studied computer science at a prestigious university or come from a 'typical' software engineering background. People from all walks of life who have a great passion for what they do can accomplish a lot.

This interview has been lightly edited for clarity.


The How I Work series asks heroes, experts, and flat-out productive people to share their shortcuts, workspaces, routines, and more. Have someone you want to see featured, or questions you think we should ask? Email Ishita.

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