Lead Software Engineer - Onsite Identification

At Klaviyo, we value the unique backgrounds, experiences and perspectives each Klaviyo (we call ourselves Klaviyos) brings to our workplace each and every day. We believe everyone deserves a fair shot at success and appreciate the experiences each person brings beyond the traditional job requirements. If you’re a close but not exact match with the description, we hope you’ll still consider applying. Want to learn more about life at Klaviyo? Visit careers.klaviyo.com to see how we empower creators to own their own destiny.

Why You Should Join the Onsite Identification Team

The Onsite Identification team is at the forefront of Klaviyo’s personalization and identity strategy, building core capabilities that drive value across our entire platform. This team’s mission is to develop highly configurable solutions for customer identifier matching—solving complex problems around tracking and storing identifiers while respecting privacy and compliance boundaries. This space is critical to enabling accurate and scalable personalization for Klaviyo customers.

As a Lead Software Engineer, you will own and drive the technical vision for this space. You will lead initiatives around probabilistic matching, integrations with first-party customer technology, and the development of robust, performant systems to support identity resolution at scale. This is a true full stack role, giving you the opportunity to solve hard technical problems both on the frontend and backend. You’ll collaborate deeply with Product, cross-functional engineering teams, and key stakeholders to shape the future of this high-value product area.

How You Will Make a Difference

• Own the end-to-end technical direction and implementation of our Onsite Identification product space.
  
  
• Build scalable, highly configurable solutions for identifier tracking and matching, addressing evolving privacy and compliance requirements.
  
  
• Lead the development of integrations with first-party technologies to enable secure data flow.
  
  
• Develop and extend probabilistic matching capabilities to improve identification accuracy.
  
  
• Partner with cross-functional teams to ensure solutions fit seamlessly within Klaviyo’s broader personalization and data platform.
  
  
• Mentor and lead engineers within the Onsite Identification team, driving technical excellence and knowledge sharing.
  
  

Who You Are

• Experienced full stack engineer comfortable building across the frontend and backend (50/50 split).
  
  
• Proficient in Python OR other core backend languages.
  
  
• Strong proficiency with React and TypeScript
  
  
• Deep understanding of distributed systems and infrastructure; hands-on experience with asynchronous queues (RabbitMQ, Kafka, Pulsar).
  
  
• Proven experience building and deploying solutions on AWS (hard requirement).
  
  
• Comfortable working with relational databases; experience with MySQL is a plus.
  
  
• Experience collaborating across teams and managing multiple stakeholders.
  
  
• Strong product mindset—excited about owning a space end to end and driving customer success.
  
  
• Experience building third-party JavaScript solutions is a plus.
  
  

Technologies We Use (not exhaustive)

• React, TypeScript
• Python
• MySQL
• Pulsar
• AWS
• Redis
• Kubernetes

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

Massachusetts Applicants:
It is unlawful in Massachusetts to require or administer a lie detector test as a condition of employment or continued employment. An employer who violates this law shall be subject to criminal penalties and civil liability.

Our salary range reflects the cost of labor across various U.S. geographic markets. The range displayed below reflects the minimum and maximum target salaries for the position across all our US locations. The base salary offered for this position is determined by several factors, including the applicant’s job-related skills, relevant experience, education or training, and work location.

In addition to base salary, our total comp