Senior Software Engineer - Profiles, Lists and Segments Boston, MA

Overview Why You Should Join the PLS (Profiles, Lists and Segments) Team: The PLS team is responsible for building and scaling the core customer data experiences at Klaviyo — profiles, lists, and real-time segments . We own the tools that let customers understand who their users are, group them into meaningful audiences, and keep those audiences up to date as new data flows in. Our work underpins how customers target, personalize, and measure every message they send, making this product area core to Klaviyo’s continued success. As a Senior Software Engineer on the team, you’ll play a key role in designing and building scalable systems that power how customers manage and activate their data. Partnering closely with product managers, data scientists, and other platform teams, you’ll help define scope, translate complex data and UX problems into practical implementations, and build intuitive workflows that give customers confidence in their audiences. This role leans frontend, with a strong focus on crafting thoughtful, reusable components and seamless user experiences using technologies like TypeScript, React, Python, and Django. There are ample opportunities for growth given the scope of this role and the team’s central role in Klaviyo’s product. How You Will Make a Difference You will be a core member of the PLS team, working on impactful customer-facing features that will make our product the best in the industry. You will work on creating easy-to-use editors that are highly performant. You will work closely with Product, Design, and Data Science to provide the best experience for our customers. You will mentor team members and drive initiatives that help the team learn new skills. Who You Are 5+ years of experience in full-stack development with strong hands-on skills in React, Redux, JavaScript, HTML, and CSS, along with familiarity with general web best practices. Has a track record of delivering and shipping work powered by or accelerated through AI. Experience conducting code reviews and running a robust testing cycle using automated testing practices and frameworks, including end-to-end and integration tests (e.g., cypress, pytest). Experienced with RESTful and GraphQL APIs, and evolving APIs and data models to support product success. You take ownership of your work—from requirements and edge cases to implementation and testing—and are motivated by solving tough problems with others. Proven track record of leading complex, multi-quarter projects involving cross-team collaboration and being accountable for their outcomes Technologies We Use (not exhaustive) React, TypeScript, Redux Python, Django Amazon Web Services (EC2, RDS, Aurora, S3, etc.), Terraform, and other DevOps tools MySQL, RabbitMQ, Redis, ProxySQL We use Covey as part of our hiring and / or promotional process. For jobs or candidates in NYC, certain features may qualify it as an AEDT. As part of the evaluation process we provide Covey with job requirements and candidate submitted applications. We began using Covey Scout for Inbound on April 3, 2025. Please see the independent bias audit report covering our use of Covey here #J-18808-Ljbffr