Software Engineer, API Platform at Horizon3 AI (United States)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.

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.

• 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

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 with gRPC and protobuf-defined service contracts

Travel Required We are a fully remote company, and this job may require up to 5% of travel to be successful.

At Horizon3, we believe that our people are our greatest asset, and our compensation philosophy reflects this core value. We are committed to fostering an environment where all employees feel valued, respected, and rewarded for their contributions. Our compensation structure is designed to be fair, competitive, and transparent, ensuring that every team member is recognized and compensated equitably across roles, levels, and locations. In accordance with various State's transparency regulations, we provide the following salary range information for this position:

• Base salary range: $148,750 - $190,000 annually. The exact salary will be determined based on the selected candidate's location, qualifications, experience, and relevant skills.
• Additional compensation: All full-time roles are eligible for an equity package in the form of stock options.

• Inclusive Team: We value diversity and promote an inclusive culture where everyone can thrive.
• Growth Opportunities: Be part of a dynamic and growing team with numerous career development opportunities.
• Innovative Culture: Work in a collaborative environment that encourages creativity and out-of-the-box thinking.
• Hybrid & Remote Work: We embrace a mix of remote and hybrid work models depending on role and location, including our Chicago office, where some roles require regular in-office presence.
• Competitive Compensation: We offer competitive salary, equity and benefits. Our benefits include health, vision & dental insurance for you and your family, a flexible vacation policy, and generous parental leave.

You Belong Here Horizon3 is not just an equal opportunity employer - we are a community that values diversity, equity, and inclusion as fundamental principles of our culture and success. We are dedicated to fostering a workplace where everyone feels welcome and respected, regardless of race, color, religion, sex, national origin, age, disability, veteran status, sexual orientation, gender identity or expression, genetic information, marital status, or any other legally protected status by law. Our commitment to diversity and inclusion means we strive to attract, develop, and retain a workforce that reflects the varied communities we serve. We believe that diverse perspectives drive innovation and strengthen our ability to create cutting-edge cybersecurity solutions. At Horizon3, every team member is valued and supported in an environment that encourages personal and professional growth. We welcome candidates from all backgrounds and experiences, and we encourage all qualified individuals to apply. Come be a part of Horizon3, where your unique contributions are recognized, and your potential is limitless.

Other Duties Please note this job description is not designed to cover or contain a comprehensive listing of activities, duties or responsibilities that are required of the employee. Duties, responsibilities, and activities may change at any time with or without notice.

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