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

Klaviyo Inc.; Boston (MA); On-site; USD 120,000 - 150,000; Full time

Job summary

A leading tech company is seeking a Senior Software Engineer to join their Profiles, Lists, and Segments (PLS) team. This role is pivotal in creating scalable systems that allow customers to manage their data effectively using technologies like React, TypeScript, and Python. You will collaborate closely with Product, Design, and Data Science teams, mentor colleagues, and lead projects to improve customer experiences. Ideal candidates should have 5+ years of experience in full-stack development with proven leadership in delivering complex projects.

Qualifications

• 5+ years of experience in full-stack development with strong skills in React, Redux, JavaScript, HTML, and CSS.
• Experience conducting code reviews and using automated testing frameworks.
• Proven ability to lead complex, multi-quarter projects with cross-team collaboration.

Responsibilities

• Design and build scalable systems for customer data management.
• Create user-friendly high-performance editors.
• Mentor team members and lead skill development initiatives.

Skills

Full-stack development

React

Redux

JavaScript

HTML

CSS

Automated testing

RESTful APIs

GraphQL APIs

Tools

Amazon Web Services

Terraform

MySQL

RabbitMQ

Redis

ProxySQL

Job description

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

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