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Software Engineer II - Flows

Onsite in Boston, MA 5 days a week

Flows is how tens of thousands of brands automate their marketing on Klaviyo, from welcome series and abandoned-cart reminders to complex multi-channel journeys that reach 100M+ consumers. The Flows Experience team builds everything a marketer touches in a flow: the canvas, triggers, filters and actions they configure, the analytics they use to decide what to do next, and the APIs that developers and AI tools use to build flows for them.

Our mission: Flows should be the easiest, most trusted place to run sophisticated marketing automation. Complex journeys should feel simple, mistakes should get caught before they cost revenue, and the product should keep up as an account grows.

We want a Full Stack Engineer who likes owning features end to end, from the React canvas down to the Python services and APIs underneath. You’ll work closely with Flows Platform, the team that runs the engine behind every flow, and with product and design, to ship work customers notice right away. Recently the team made large flows open up to 70% faster, launched an API (also in the Klaviyo MCP) that lets developers and AI agents safely edit live flows, and raised webhook throughput 20x.

How you’ll make a difference

Own major parts of the Flows product (the builder, analytics, version history, management surfaces) from design through launch and operation
Design and evolve the public and internal Flows APIs that define how a flow can change. Customers, partners and AI agents all build on them.
Make the product fast and reliable for very large flows and very large accounts, whether that means canvas render performance, a slow analytics query or an API under heavy load
Build guardrails that catch mistakes before they cost a brand revenue: validation, safe defaults, clear feedback and easy recovery
Partner with Flows Platform on the contract between the product and the engine, so new capabilities scale from day one
Raise the bar for your team as a technical leader through design reviews, mentorship, operational excellence and modern, AI-assisted ways of building

Who you are

You’ve built and shipped products that customers rely on, and you care about the user experience as much as the code
You’re strong across the stack. You know at least one area deeply (complex front-end apps, API design, or backend performance) and are comfortable working in the others.
You enjoy hard problems at the line between UX and systems: a canvas that lags with 200 nodes, a workflow with too many clicks, a query that times out, a queue that won’t drain
You ship early and often, use data and customer feedback to iterate, and work closely with product and design
You thrive on a small, autonomous team where you own outcomes and collaborate widely to get them right
You’re curious about how AI changes both what we build (agents that build flows) and how we build it

Technologies we use (not exhaustive)

React, TypeScript, JavaScript
Python, Django, Celery
MySQL, Redis, RabbitMQ, Kafka
AWS, Terraform, and modern observability and CI/CD tooling

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.