Our interview with Slack's co-founder and CTO, Cal Henderson. Recorded Sept 19th, 2025.| Building Slack
“If we can’t ship safely, we aren’t shipping at all,” Cal Henderson wrote in our #announce-devel channel. It was September 2018. We had just recovered from our second major self-inflicted outage in a period of weeks. Slack – after experiencing an extended period of| Building Slack
One of the four big bets in Stewart’s Master Plan was to make Slack a network. We initially designed Slack to be used for a company’s internal communication. Any company would still have plenty of inbound and outbound communication with the wider world: customers, vendors, contractors,| Building Slack
Eric Costello co-founded four products at two companies with Stewart, Cal and Serguei. Ludicorp made Game Neverending and Flickr. Tiny Speck made Glitch and Slack. Eric was there for all of it, the coding engine behind the frontend for all of these products that millions of people loved. Understandably, Eric| Building Slack
[This post is about the day that Glitch failed, and how that failure created the opportunity to make Slack. We're sharing it here (out of chronological order) to mark 12 years since the famous pivot.] “We have to shut down the game.” Stewart Butterfield said. I| Building Slack
Working with bigger companies meant figuring out how to plug ourselves into lots of standard big-company processes. One of the processes we had to learn was how to tell customers how much money they owed us so that we could get paid. We needed to generate invoices. Cal wrote the| Building Slack
When it came time to build Slack, we wanted to capture the best parts of IRC in the context of running a business, add all of those ancillary services as native features, and vastly expand the group of people with whom our product could be friends.| Building Slack
Stories of building Slack — the company, the product, and the business — by two people who were around for the entire journey.| Building Slack
On the morning of November 2nd, 2016 we arrived to the office to find a paper copy of the New York Times on our desks. In it was a full-page ad welcoming Microsoft to the market that Slack had created. Not coincidentally, Microsoft would announce the launch of their new| Building Slack
Ali Rayl knew Slack’s customers better than anyone. As Slack’s first customer support staff, Ali personally answered every ticket during our early alpha and beta rollouts. She was in the weeds of every front line issue as the customer support team grew along with our user base. Over| Building Slack
Backstage, Stewart vibrated with his typical charismatic energy. An assistant checked his lapel mic. Everyone in the company, now numbering nearly 500 people in early 2017, awaited him. He was ushered on stage to enthusiastic applause from the crowd and expectant video participants from our offices around the world. Slack's| Building Slack
We did many things fairly well at Slack. One thing we never did well, however, was figuring out how much office space we’d need. We outgrew our Clementina Street office in July of 2014, just five months after launch. Our new office in a freshly renovated building on Folsom| Building Slack
We launched Slack to the world on February 12th, 2014. Thirteen months after starting work, nine months after releasing our early alpha version, and six months after starting our preview release. We crossed the finish line we'd been sprinting toward for the last year, not fully realizing that we were| Building Slack
From John O'Nolan (CEO of Ghost): How did Stewart's infamous "we don't sell saddles here" essay go down internally, at the time? And how do you feel that essay aged, with hindsight? Stewart shared We Don't Sell Saddles Here internally in July 2013, just before we launched our Preview Release.| Building Slack
It was the fall of 2013. Barack Obama was President. Game of Thrones had finished its third season. The red wedding shocked us all. WeWork was worth $440M, and Uber surpassed unicorn status with an eye-popping $3.7B valuation. MoviePass let you see as many movies as you wanted in| Building Slack
By the summer of 2013, we knew we were on to something. The people we’d asked to try Slack – at Silicon Valley tech companies like Rdio, Medium, and ThatGameCompany – were still using it. And they were telling their friends to use it. Small teams within companies started spreading it| Building Slack
As we got started committing ideas to code, we already knew the utilitarian aspects of Slack would work — our own team had proven it through years of use. IRC and other chat apps had dedicated followings. It was clear that Channels and DMs with integrated files and search worked better| Building Slack
Eight of us sat around an old wooden table in Tiny Speck’s Vancouver office. Cardboard boxes and dead batteries were scattered around the abandoned desks of our former colleagues. The place felt big and empty. We’d shut down Ur — the world of Glitch — a month before. We were| Building Slack
