Senior Software Engineer, Agentic Systems

At Horizon3, we’re building a team of bold thinkers, problem solvers, and Learn-it-Alls.
We’re looking for individuals who:

Love solving tough problems
, especially the ones no one else has cracked.

Thrive in high-performing teams that celebrate success and lift each other up.

Have the grit and tenacity to take on complex, mission-critical challenges.

Want to make a real impact by helping organizations stay ahead of attackers.

Continuously learn and adapt
, embracing new technologies, perspectives, and ideas.

Are passionate about disruption
, driving innovation in the cybersecurity space.

If you’re eager to grow, driven to contribute, and ready to shape the future of cybersecurity, we want to hear from you.

The Perks of working with Horizon3

We’re a team of “learn-it-alls” who love building awesome products. From intern to CEO, we celebrate diversity and bring a wide array of experience from technology startups, Fortune 500s, and the US Military.

With offices in San Francisco, Chicago, and Amsterdam, we have hybrid and remote positions available globally.

We’re motivated to create a safer, more secure environment, convert new ideas to exceptional solutions and deliver great customer experiences.

Be part of a passionate and talented team which have entrepreneurial spirit, because it makes a huge difference.

You’ll have complete ownership and responsibility along with huge potential for growth. We envision the future and build it one step at a time.

Competitive pay, great health & dental care for you and your loved ones, and a 4 weeks + generous holidays and vacation packages globally.

We’re a remote-first company with teammates clustered around the globe.

US, Remote

Full time

Remote

Get to Know Us

Horizon3 is a fast-growing, remote cybersecurity company dedicated to the mission of enabling organizations to proactively find, fix, and verify exploitable attack vectors before criminals exploit them. Our flagship product, the Node Zero™ platform, delivers production-safe autonomous pentests and other key assessment operations that scale across the largest internal, external, cloud, and hybrid cloud environments. Node Zero has been adopted by organizations of all sizes, from small educational institutions to government agencies and Global 100 enterprises.

It is used by ITOps/Sec Ops 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, the 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.

Summary

We're building an autonomous, black-box web application penetration tester. It crawls and attacks real production websites the way a skilled human pentester would, finding broken access control, injection, XSS, SSRF, SSTI, and more, under a strict production-safe, no-false-positives mandate.

We have deep offensive expertise on this team: people who know exactly how to find and exploit these vulnerabilities by hand. What we need is an engineer who can turn that expertise into autonomous agent capability
, the reasoning, orchestration, tooling, and evaluation that lets an LLM-driven agent do this work reliably, at scale, and unattended. You'd own and evolve the attack-agent layer: the part of the system that decides what to probe, forms and tests hypotheses, exploits, and verifies, without false positives and without touching anything it shouldn't.

This is a build role, not a research role. We use models surgically,
deterministic-first, LLM-as-scalpel
, and the hard problems are in engineering reliability, not chasing benchmarks.

Essential Functions

Build and evolve the agent harness and orchestration t…