September 14, 2017
Photography by Amelia Ingraham. The interview has been edited for length and clarity.


For Klaviyo’s first five years of existence, CEO and co-founder Andrew Bialecki wrote every line of code for the company. Today, there are 80 employees at the fast-growing Boston office, and Bialecki has handed over the reigns to a talented team of engineers.

To meet Bialecki’s high expectations, the engineers constantly learn — through TED talks, lunch and learns and personalized training budgets of $3,000 per employee per year.

And how do they keep it weird? Nicolas Cage, Settlers of Catan and “sandwich theory.”


Photo via Amelia Ingraham



FOUNDED: 2012.


WHAT THEY DO: Klaviyo uses data to drive marketing. Its software helps e-commerce marketers target, personalize, measure and optimize email and Facebook campaigns.

WHERE THEY DO IT: 225 Franklin St., in Downtown Boston.

IDEAL CANDIDATES: Engineers who are eager to learn and grow, and love solving hard problems.

STACK: Python, Django, MySQL, Cassandra and RabbitMQ. They leverage Amazon Web Services extensively, along with other Amazon services like Aurora MySQL and EC2 Autoscaling.

HALF A BILLION: The number of emails Klaviyo plans on sending this Black Friday, the biggest day for e-commerce sales.


Photo via Amelia Ingraham


What does Klaviyo’s engineering team do?

Andrew Kenney, vice president of engineering: Klaviyo’s mission in a nutshell is to help ecommerce companies make more money by having more engaging and personalized relationships with their customers.

We build platforms that help entrepreneurs tap into the data they already have. This helps them reach out and sell more products to customers and find more customers to engage. We do all the heavy lifting by figuring out how they can make more money.

What does Klaviyo look for in engineers?

Laura Stone, senior site reliability engineer: The CEO, Andrew Bialecki, is also our technical founder and he likes to interview as many engineers as possible. Something that drew me to him was when he said, “We’re all about growing.” Klaviyo looks for engineers who maybe don’t know the Python language we use, but are smart people who want to grow and take on really interesting challenges.

Kenney: We look for people who are not afraid of learning the nitty gritty of how our systems are built and understanding the performance characteristics of how to build something to scale. When you’re working with a high-growth startup, you have to think about scaling not just billions of records but trillions. You have to want to find ways to break through to new customers.


Photo via Amelia Ingraham


Can you give me an example of a problem you solved?

Chris Conlon, developer: Deliverability. Jake Cohen (director of product management) became the deliverability expert. We trust him over anyone externally at this point. If one of our customers is having trouble getting an email into someone’s inbox, Jake and the team can figure out why. It’s been a pain point for a lot of people using the platform who might be using it incorrectly or have cultivated bad sending habits.

Kenney: One goal we have is helping companies increase their audiences. Not by having lists of tens of thousands of email addresses, but by capturing people through novel marketing campaigns. We ask, “How can we find the right segment of people who might engage with our new initiative?”

What is the breakdown of a developer's day? For instance, how much time is there for support or troubleshooting, and how much time for coding or analyzing requirements?

Andrew Kannan, software engineer: It really depends on what your current project needs. The majority of the time, we’re coding — definitely more than 75 percent of the time. We also work closely with the product team to get certain features really fleshed out. Working closely with them makes it really easy to nip problems in the bud.

Chris: Each team determines the best way for it to manage its workflow. We all have similar workloads but we approach them differently. In several weeks, when we are doing different work, our workflow might change again.

Laura: Also, people spend a lot of time communicating, either asynchronously via Slack or pairing together, having someone look over their shoulder and saying, “How does this look?” We do a lot of code reviews.


Photo via Amelia Ingraham


What is the biggest challenge you’re facing?

Kannan: There’s lot of stuff we want to accomplish and a limited number of people. There’s no lack of work — and these are good, interesting, hard problems. There’s always more projects we want to work on, but you need more people to move faster.

Laura: The CEO wrote all of the code for Klaviyo for the first five years of its existence. This is pretty amazing, but the problem is, you start onboarding all these new people and he can’t spend his time coding anymore. So there’s a knowledge transfer problem. How do we go about scaling and re-factoring these systems while learning about them at the same time?

How are you preparing for your two biggest days of the year, Black Friday and Cyber Monday?

Laura: Two of the four engineering teams are now focused exclusively on scaling the system for Black Friday on the tech front but also on the people and process fronts. Our tech teams are building the platform in a box so that any engineer can use it to spin out a production-like system of Klaviyo and run tests against it. We’ve been developing not one but two load testing tools to run load and stress tests against a production-like system to be sure we can hit the numbers of emails we send over an hour and to be sure that by Black Friday, we can hit half a billion emails.

What is the most innovative thing about Klaviyo’s technology?

Kannan: The way we represent our data. The way we use the Cassandra database to split up all of our data and the way we represent properties of a customer for any given company.

Kenney: Some key decisions that were made early on have really paid off. We have an end-to-end platform so we’re not just an API. We offer all of the integrations to make Klaviyo super friendly. Customers don’t need to hire a developer to tap into their email platform; they can plug into it in minutes.


Photo via Amelia Ingraham


I've heard that everyone at Klaviyo learns a new skill or tool every six months. Can you give some examples?

Chris: I have not stopped learning since coming to Klaviyo. I most recently attended the Percona Live Open Source Database Conference and was thrown into newer DevOps skills. I packed a notebook full of things I thought could benefit the Klaviyo platform but also just things I wanted to look into. The knowledge was super beneficial to me personally but I also disseminated my notebook to the team and have given lessons at our weekly TED talks. I could probably use this notebook till I’m an old man.

Any fun engineering team traditions?

Chris: Nicholas Cage is our spirit animal. He makes an appearance in every TED talk we have. Why? Because he’s the finest actor of his generation.

Laura: We also spend a lot of time on “Sandwich Theory,” where we ask ourselves, “What exactly is a sandwich?” It’s the number one productivity killer. Is a burrito a sandwich? No. Basically, there are ingredient purists and structural purists, but you get the picture.

Can you pinpoint a moment that reaffirmed your decision to work here?

Kannan: The thing that sold me on Klaviyo was that the engineering culture is pervasive throughout the entire company, not just the engineering team. The second thing that sold me on Klaviyo was that our CEO is an engineer. There was a month where the VP of engineering was out on paternity leave and the CEO came in and helped out. Seeing his engineering chops and the excitement he has for our product was really infectious.

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