← All roles

Senior Software Engineer, Browser Automation

Horizon3 AI· Engineering
Apply on company site
Remote$199k - $235kFull-timePosted 4mo ago

About the role

Senior Software Engineer focusing on building and hardening Horizon3’s browser automation and crawling engine to enable autonomous, production-safe web application penetration testing at scale using Playwright/Stag ehand, advanced authentication flows, and potential LLM-in-the-loop navigation.

Responsibilities

  • Help us grow and harden our browser automation and crawling engine, the layer that discovers, navigates, and interacts with target applications before and during an autonomous pentest.
  • Advance our browser-driven crawler using Playwright and Stagehand.
  • Tackle the realities of modern web apps: SPA routing and hydration timing, authenticated sessions, multi-step flows, file uploads, WebSocket/Socket.IO traffic, infinite scroll, and crawler traps.
  • Extend agentic login and authentication capabilities, including complex auth flows, MFA/TOTP, and credentialed access reliable enough to run unattended against customer environments.
  • Improve crawl coverage, determinism, and throughput (endpoint/parameter discovery, dedupe, queueing, state management) while staying production-safe and side-effect-aware.
  • Help balance deterministic automation with LL M-driven navigation, applying models judiciously for speed, debuggability, and cost.
  • Collaborate with attack-team engineers who consume crawl output and help shape the graph-backed application map the pipeline depends on.

Qualifications

  • Experience building production software with deep, hands-on browser automation (Playwright, Puppeteer, or Selenium) against real, non-trivial web applications.
  • Strong TypeScript / Node.js skills and comfort with headless-browser stack, Chromium internals, Chrome DevTools Protocol, network interception, DOM, and JS execution contexts.
  • Track record of taming flaky, stateful, JavaScript-heavy apps, including SPA timing, authentication, and anti-automation defenses.
  • Solid instincts for distributed/concurrent systems: queues, backpressure, retries, idempotency, and running many browser sessions reliably at scale.
  • Bias toward determinism and debuggability, and prudent use of LLMs only when deterministic approaches fail.
  • Ownership mentality and comfort taking a subsystem from basic working to unattended-scale operation.

Skills

Required:Browser automationTypeScript / Node.jsDistributed/concurrent systemsDeterminism & debuggability

Benefits

  • Inclusive Team culture
  • Growth opportunities
  • Innovative culture
  • Hybrid & Remote Work with some roles requiring in-office presence in Chicago
  • Competitive compensation including equity and benefits (health, vision & dental, flexible vacation, parental leave)
Last updated Oct 8, 2026. Interested? Apply on the company site.

About Horizon3 AI

Only Pentesting Platform Proven in Production

Continuously assess, fix, and verify your security posture. Securing enterprises across many attack surfaces.

PentestingSecurity PostureThreat DetectionVulnerabilitiesRisk AssessmentOffensive Security
Company profileWebsite

More open roles at Horizon3 AI