Senior Full-Stack Engineer

Senior Software Engineer (EMEA) Born out of the heart of the Basque Country in Bilbao, ZenRows is one of the fastest-growing startups in Europe! We work 100% remotely and believe in hiring the best people, no matter where you are in the world!    Founded in 2021, our mission is to transform the future of data workflows by enabling seamless, large-scale data extraction from the web. With our powerful tools, businesses can automate data collection at scale while leveraging the most advanced anti-bot bypass system on the market. Thousands of companies worldwide—across industries like e-commerce, real estate, finance, and AI—rely on ZenRows to streamline their data pipelines, fueling automation, analytics, and AI-driven insights   As we continue our rapid expansion, we are now looking for a Senior Software Engineer to join us on a permanent basis and make an instant impact.  THE ROLE:  We’re looking for a Senior Software Engineer to join our Stealth & Reverse Engineering team—the elite force responsible for making our headless browsers and traffic completely undetectable by modern anti-bot systems. You will own and evolve our custom fork of Chromium, continuously identifying and patching all behavioral and fingerprinting vectors that reveal automation. You'll go deep into browser internals, reverse engineer anti-bot defenses, and create a fully cloaked browsing experience across real-world targets. You’ll also build internal tools that detect, analyze, and resolve JavaScript-based bot challenges (like fingerprinting, integrity checks, proof-of-work, and obfuscation traps), and help automate evasions across our infrastructure. This is a deeply technical, adversarial, and high-leverage role at the heart of what makes our scraping infrastructure world-class. We’re a remote-first company with a fast-paced, high-impact culture. In this role, you’ll work closely with our CEO, Aurken, and our Director of Engineering. And as a business with two technical founders who have strong engineering backgrounds—you must be comfortable engaging in technical discussions while balancing business needs. KEY RESPONSIBILITIES: 🧬 Browser Fingerprinting & Chromium Patching * Own and evolve our Chromium fork, maintaining full control over browser behavior and instrumentation. * Patch and neutralize browser fingerprinting surfaces: canvas, audio, WebGL, screen, navigator, user agent, and more. * Harden the browser against integrity checks (function.toString, error stack traces, memory layout, etc.). * Ensure parity with real users under advanced detection tools like FingerprintJS, Datadome, PerimeterX, and others. 🔬 Reverse Engineering & Challenge Automation * Analyze real-world JavaScript challenges and traps designed to detect bots. * Reverse engineer obfuscated payloads and evasive scripts using tools like Chrome DevTools, Frida, Wireshark, mitmproxy, etc. * Build internal tooling to automatically detect, triage, and solve bot challenges, integrating into our scraping runtime. * Develop detection signatures for new anti-bot mechanisms and continuously track vendor evolution. 🧰 Internal Tooling & Automation * Build robust internal libraries to spoof browser behavior, intercept and manipulate DOM/state, and bypass anti-bot logic. * Create automated pipelines that detect detection, trigger browser patches, or escalate to manual review. * Integrate JavaScript instrumentation and DOM mutation trackers to flag stealth issues before customers do. 📊 Observability, Resilience & Safety * Build internal dashboards to monitor fingerprint mismatches, challenge rates, JS errors, and detection spikes. * Proactively identify and mitigate stealth regressions caused by Chromium updates or vendor changes. * Help maintain and evolve our internal stealth testbed, simulating dozens of anti-bot vendor environments. 🧠 Technical Leadership & Deep Expertise * Be the team’s go-to expert in browser internals, bot detection evasion, and security-focused reverse engineering. * Mentor engineers in topics like V8 internals, JS fingerprinting, and browser automation stealth. * Help define our long-term strategy around browser-level evasion and undetectable scraping at scale. THE PERSON:  You’re the kind of engineer who doesn’t just use tools—you tear them apart to understand exactly how they work. You’re fluent in browser internals, and you treat anti-bot systems as adversaries to outsmart. You’re comfortable working in the gray areas of web security, JavaScript instrumentation, and reverse engineering. You love automation, can write clean low-level code, and know how to survive in hostile runtime environments. This role is for a rare breed of engineer who’s part hacker, part builder, and 100% obsessed with invisibility. KEY SKILLS AND EXPERIENCE: * 5+ years of software engineering with a focus on browsers, reverse engineering, or automation in adversarial environments. * Fluency in C++ and JavaScript (Node or browser), with ability to write clean, testable low-level code. * Deep understanding of Chromium internals: Blink, V8, DevTools Protocol, browser architecture, etc. * Proven experience patching Chromium or building hardened browser automation setups (e.g., stealth plugins, puppeteer-core forks). * Advanced knowledge of JavaScript fingerprinting, detection vectors, and browser inconsistencies. * Familiarity with anti-bot vendors like PerimeterX, Datadome, Kasada, Akamai Bot Manager, and FingerprintJS. * Strong debugging and tooling skills: Chrome DevTools, Wireshark, mitmproxy, Frida, Objection, or similar. * Experience automating evasion workflows and detection pipelines is a major plus. * Communicate clearly, document thoroughly, and guide complex decisions across teams. Bonus Points If You * Have built your own Chromium fork or stealth layer from scratch. * Have hands-on experience defeating real anti-bot challenges and captcha solving  in production environments. * Know how to simulate mouse/keyboard behavior and DOM interaction that mimics real humans. * Have published research or tools related to browser automation, anti-bot evasion, or JavaScript analysis. * Knowledge of WebAssembly, memory layout inspection, syscall monitoring, or other stealth-adjacent low-level domains. AGILE & PROCESS-DRIVEN MINDSET * You optimize workflows, reduce bottlenecks, and improve efficiency without overcomplicating processes. * You understand the Pareto principle (80/20 rule) and prioritize high-impact work over perfection. * You are used to working with multidisciplinary teams and balancing engineering, business, and product needs. STRONG PRODUCT & BUSINESS AWARENESS TRANSPARENCY & COLLABORATION * You thrive in open, honest communication and ensure visibility across teams.  * You can handle strong opinions from technical founders and have the guts to say no when needed,while gathering input from multiple stakeholders * Excellent communication skills, with the ability to convey complex technical concepts to non-technical stakeholders. Why you will love working here…   * Our people crave ownership and opportunity over everything else. We offer responsibility and scope to do things in your role that you can only dream of in similar roles in larger companies. * We have a CEO who values world-class talent over everything else. Trust and respect are earned, and with them come reward and recognition like nowhere else. * In a world where it feels like everyone is being called back to being in an office, we operate a truly 100% remote approach that allows you to work from anywhere you choose.  Forget Agile, Scrum, Lean... or whatever development methodology is trendy this week. We give you a horizontal view that enables you to identify where you think you can contribute the most. * We have fun! The above may sound like we are all about work, but we put a lot of focus on ensuring our culture is one that our people enjoy, which lets you build lasting friendships and grow both personally and professionally. What rewards and benefits would I get in this role? * 100% remote work: We are a company that offers true freedom. Work wherever life takes you. * The salary you are worth:  We never ask people what they are earning, but instead what they are looking for. If your ability and experience justifies it and we think you will help us succeed, then we will match your expectations. * The equipment you want: We believe in giving our people the tools they need to succeed and don’t have a default machine to give you. * Generous Learning & Development budget: We believe in always adding value to our top performers and helping them grow their skills in a direction that is beneficial both to them and the business * All-Star Awards: We recognize achievements in many ways within the business, but the bi-annual All-Star Awards allow the CEO to tailor reward packages to the person. Whether this is a holiday destination of choice, a learning course that adds value or something else.. We believe in getting to know every employee personally. * BitWarden Account: With employees working remotely worldwide, we are keen to ensure we empower them with tools to keep passwords as secure as possible. * Charity Initiatives: We are a business that believes in giving back to the community, and every year, we allow our employees the opportunity to give back. * Annual Kick-Off: We want our employees to see where ZenRows was born and enjoy all the Pintxos they can handle. * Share in Our Success:  We want our top performers to be part of the company's success and offer opportunities for stock option allocation when people show their value. * Deel Benefits: As a fully remote organization, we employ our people via Deel. This brings freedom of location and many other benefits, including discounts on VPNs, memberships and services.    Values  We are proud of our uniquely agile, fast-paced, and autonomous environment. Our core values of Ownership, Dedication, Impact, Transparency and Agility run through everyone who works for us, and everything we do. We are a sociable company and don’t let a fully remote model stop us from feeling connected to the place we work and the people we work with. The atmosphere across the business is friendly and supportive, with a constant desire to improve in everything we do!  Diversity, Equity and Inclusion Here at ZenRows, we are committed to diversity, equity and inclusion but recognise that we can always do more. Every job description is subject to scrutiny through a gender bias decoder, ensuring our roles are as inclusive and attractive as possible. Our culture is one that aims to nurture a welcoming and safe working environment for everyone with initiatives that embrace our globally diverse family. We are committed to protecting the mental health of our employees and aim to create a great place to work, whoever you are and wherever in the world you work from. https://www.zenrows.com/careers Privacy and Your Data   At ZenRows, we prioritize the privacy and security of data entrusted to us. We are committed to complying with all applicable data protection regulations and industry best practices. As part of our team, you will contribute to creating and maintaining systems that uphold the highest data integrity, confidentiality, and transparency standards. Your role will help ensure that we continue to protect sensitive information, foster trust with our customers, and support a privacy-first culture across our organization.   Any job offer we may make to you will be subject to your successfully passing background checks.