QA Engineer — System & Performance Testing

Do you enjoy taking a complex system apart to find where it breaks under load? Are you the type who’d rather verify estimates on real hardware than just trust them on paper?

We’re looking for the first person in a dedicated QA role to help us take our testing to the next level. Until now, system-level testing has been handled by individual teams on their own – now we want someone to own this area, connect the dots, and give it a clear direction.

We’re GREYCORTEX. We develop Mendel, an on-premise network security solution that protects the infrastructure of banks, hospitals, and industrial organizations. The product is complex, runs on real hardware at customer sites, and processes tens of terabytes of data.

What you’ll be doing

Own and run release testing – define test scope, coordinate with teams, evaluate results.
Design and execute performance and sizing tests – as in “can Mendel handle 1M hosts on this hardware?”
Validate Mendel’s compatibility across different environments – proxies, APIs, network configurations, new vendor hardware.
Gradually build a systematic, repeatable approach to performance testing – turn ad-hoc requests into a proper process.
Plan test hardware utilization and maintain test environments.
Document and report results clearly – for developers and non-technical stakeholders alike.

Who we’re looking for

A hands-on practitioner with a technical background who can organize their own work and see things through. You don’t need 15 years in QA – but you do need real experience testing complex products and a solid understanding of what’s happening under the hood.

Must-haves:

Experience with performance or system-level testing – load testing, benchmarking, monitoring (T‑Rex, Grafana, Munin or similar).
Solid hardware fundamentals – you know how CPU, memory, NICs, and storage interact and what that means for system performance.
Working proficiency in Linux – you’re comfortable in CentOS environments and can troubleshoot confidently.
Basic knowledge of network protocols – you’re familiar with protocols such as TCP/IP, DNS, HTTP, LDAP, TLS, and similar. You understand what’s happening in the network and can translate that into what it means for testing a network security solution.
Analytical thinking – you can take a customer use case and translate it into a concrete test scenario.
Cross-team communication – clear, factual, no unnecessary drama. Engineering, product, support, sales – you can work with all of them.
Systematic mindset – you naturally build structure, documentation, and order in your work.

Experience with vulnerability testing (Nessus, Qualys, OpenVAS or similar) and an interest in cybersecurity would be a major plus – in the context of our product, it will help you get up to speed faster and push the quality of the solution forward.

Why you might enjoy this

You’re the first person in this role – you’re building something that didn’t exist before.
Your work will directly impact the quality of a product that protects real infrastructure.
You’ll have the space to approach things your own way.

What you can look forward to

5 weeks of vacation + 4 sick days
Flexible working hours – we work mainly from our Brno office, ideally 3–4 days a week. Plan for a full on-site presence at the start of onboarding.
Annual bonus – based on company performance
Education budget – courses, books, conferences that matter to you
Multisport card contribution – for clearing your head
Meal allowance, laptop, phone plan
English lessons – individually or in groups.
Team events – board games, BBQ, beers together

We are looking for a colleague for the position of