Senior Software Engineer

Overview

Klaviyo is growing fast and we have openings for all skill levels across all of our teams. Learn more about our engineering culture at (Use the "Apply for this Job" box below)..tech

We love tackling tough engineering problems and look for Engineers who specialize in certain areas but are passionate about building, owning & scaling features end to end from scratch and breaking through any obstacle or technical challenge in their way. We push each other to move out of our comfort zone, learn new technologies and work hard to ensure each day is better than the last.

Klaviyo operates a real-time data platform coded in Python built for massive scale on Amazon Web Services (AWS). Engineers come to Klaviyo with experience in a variety of languages and from a number of disciplines.

DevX is a hybrid product–platform team focused on empowering external developers and partners by supporting applications they build on top of Klaviyo’s Public APIs and features. Examples of these areas of ownership include:

• our Application directory, which is used to promote and allow Klaviyo customers to discover applications that they can enable for their account
• the self-serve application process for a Partner to submit an Application and the ability for Klaviyo staff to review and approve an Application
• API Analytics is a system used by developers and partners to diagnose issues in their applications and understand their API usage. It is powered by a near real–time data pipeline that processes over 160,000 events per second.
• Autogenerated API docs, SDKs, CLIs & MCP servers

You will have an opportunity to make a major impact on the direction and priorities of the team.

As an engineer on this team, you will work on Klaviyo’s app marketplace, application publishing workflows, and the developer-facing tools and systems that support our app ecosystem. Additional responsibilities include providing quality PR reviews for our code-owned areas of the application, collaborating with product owners and providing technical expertise on upcoming Product Specifications, and participating in the definition of well-defined, estimated, and planned scopes of work.

• 5+ years of experience in a software engineering discipline
• Experience with full stack application development
• Experience working with both monolithic and microservices architectures
• Experience with CI/CD pipelines
• Experience debugging performance issues and improving application performance
• Python
• React, React Query
• Document DB
• Clickhouse
• JSON Forms
• Redis
• Memcached
• Rabbit
  
  MQ / Celery / Apache Pulsar

• Experience working with Service Oriented Architecture (preferably in Python)
• Experience working with RESTful applications/APIs/gRPC

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 compensation package may include participation in the company’s annual cash bonus plan, variable compensation (OTE) for sales and customer success roles, equity, sign-on payments, and a comprehensive range of health, welfare, and wellbeing benefits based on eligibility.

Your recruiter can provide more details about the specific salary/OTE range for your preferred location during the hiring…