Staff Software Engineer - Detection Platform

About Castle

Castle is building real-time infrastructure to protect SaaS platforms from fraud, abuse, and malicious automation. Our product stops bots, detects account abuse, and helps teams fight sophisticated attacks without slowing down real users.

We’re trusted by companies like Canva, Atlassian, and Rockstar Games, and backed by Y Combinator, Index Ventures, and top-tier angels from Stripe, Datadog, and New Relic.

Detection Platform

Detection systems tend to follow a familiar arc. They start simple, then someone adds a rule. Then fifty more. Then a model. Then another model to fix the first one. Before long, nobody can explain why a request was blocked, deploys feel risky, and the team that's supposed to move fast is afraid to touch anything.

We're building the opposite. Castle's detection platform — rule engines, counters, threat intelligence lists, ML models — is designed to stay simple enough to reason about, safe enough to iterate on daily, and fast enough to run in the hot path of billions of API requests.

Our Intelligence team defines what to detect. You define how it runs. You'll co-own this platform, bridging Platform and Intelligence — shaping how the building blocks are designed, deployed, and monitored.

What you care about

The research team won't hand you a spec. They'll describe a detection problem, and you'll figure out how to solve it. But you're also the person who asks: what happens when this fails? How does it behave under load? How much memory does this cost us? That care for the platform side is what makes the difference between infrastructure that compounds and infrastructure that rots.

When researchers can ship a new detection rule during Tuesday peak hours without hesitation, that's your work paying off.

Experience

• 8+ years of professional software development in backend-heavy or platform roles — SaaS, API-first, or infrastructure environment.

• You've built performance-sensitive production systems — streaming pipelines, in-memory stores, or similar infrastructure where latency and throughput matter.

• Proficiency in Ruby and familiarity with our core stack: AWS, PostgreSQL, Kafka.

• Experience with event-driven architectures and production observability.

• Nice to have: ML model serving, security/fraud/bot detection background.

This is a fully remote role, with teammates across the US and Europe. We have offices in New York and Cracow. We expect candidates to be located between UTC-5 and UTC+1 for timezone overlap.

We pay competitive salaries, offer equity, flexible hours, unlimited PTO, and parental leave.