Software Engineer, API Platform

Get to Know Us Horizon3 is a fast-growing, remote cybersecurity company dedicated to the mission of enabling organizations to proactively find and fix and verify exploitable attack vectors before criminals exploit them. Our flagship product, the NodeZeroTM platform, delivers production-safe autonomous pentests and other key assessment operations that scale across the largest internal, external, cloud, and hybrid cloud environments. NodeZero has been adopted by organizations of all sizes, from small educational institutions to government agencies and Global 100 enterprises. It is used by ITOps/SecOps teams, consulting pentesters, and MSSPs and MSPs.  We are a fusion of former U.S. Special Operations cyber operators, startup engineers, and formerly frustrated cybersecurity practitioners. We're committed to helping solve our common security problems: ineffective security tools, false positives resulting in alert fatigue, blind spots, "checkbox” security culture, cybersecurity skills shortage, and the long lead time and expense of hiring outside consultants. Collectively, we are a team of learn it alls, committed to a culture of respect, collaboration, ownership, and results.   WHAT YOU'LL DO The Software Engineer on the API Platform team helps build the internal API layer that connects NodeZero's services and powers the interfaces that customers and integrations rely on. API Platform owns the gateway, the API contracts, and the shared platform capabilities that other teams consume — your work directly determines the reliability, latency, and developer experience of NodeZero's service mesh. You'll join a small but growing team, shipping against a roadmap that includes API consolidation, versioning, rate limiting, and observability. This role reports to the API Platform Engineering Manager. RESPONSIBILITIES - Implement and maintain API endpoints, middleware, and platform services in Go - Build and evolve the API gateway layer — routing, authentication, rate limiting, and request/response shaping - Write and maintain API contracts (OpenAPI/gRPC definitions) and communicate breaking changes to internal consumers - Contribute to service reliability: monitoring, alerting, SLA tracking, and incident response for platform APIs - Write clear, reviewable code with tests that cover both the happy path and failure modes - Collaborate with Data Ingestion, Integrations Platform, and Client Platform teams who consume the APIs you build   WHAT YOU'LL BRING BACKEND ENGINEERING - 2+ years of professional software engineering experience building production backend services - Proficiency in Python or strong motivation to ramp quickly — Python is the primary language on this team - Solid understanding of GraphQL API design principles and HTTP semantics; experience with gRPC is a plus - Ability to reason about service reliability: latency, error rates, retry behavior, and circuit breaking PLATFORM FUNDAMENTALS - Comfort working in Kubernetes-based environments — deploying, debugging, and understanding how services interact - Experience with containerized development workflows (Docker) - Familiarity with API authentication patterns (OAuth 2.0, API keys, JWT) CRAFT & COLLABORATION - You write code that your teammates can read and review without decoding — clear naming, small functions, meaningful tests - You communicate blockers early and ask for help without prompting - Comfortable working asynchronously across a distributed team   NICE TO HAVES - Experience with API gateway technologies (Kong, Envoy, NGINX, or cloud-native equivalents) - Exposure to service mesh architectures (Istio, Linkerd) - Background in cybersecurity or experience building APIs consumed by security tools - Experience wit