Principal Full-Stack Engineer, Contract in London

Who Are We?

Xcelirate develops technologically-advanced platforms which are accessed by thousands of users every minute! We are proud to offer a workplace where the sharpest developers come together to strategically plan and swiftly execute practices which see us maintain our existing market dominance and attain global expansion. We owe our success to our customers who have seen us grow across a decade, and our talented team who have made that growth possible!

What are we looking for?

You’re a principal-level full-stack engineer. You haven’t just been around the block – you helped decide which blocks were worth building, and which ones should’ve been bulldozed early.

At this point, programming languages don’t really impress you anymore. You treat them as tools that translate intent into something a compiler or interpreter can run, choosing them pragmatically, discarding them without nostalgia, and never confusing syntax or novelty with actual progress.

You’ve been around long enough to remember when PHP constructors shared their class names, when exceptions were returned instead of thrown, and when Yeoman, Underscore, and CoffeeScript felt like the obvious future. More importantly, you also learned when to stop using those awful, awful creations.

Despite all that experience, you’ve stayed deeply hands-on, and you’ve never been particularly interested in drifting into management just because that seemed like the default next step. You’re still happiest close to the code.

You bring a distinctly stoic approach to your work. You don’t panic when systems misbehave, you don’t chase drama, and you don’t confuse urgency with importance.

When you join a project, things tend to settle down. Code becomes easier to reason about, systems start to feel calmer, and decisions get clearer. That sense of clarity tends to spread to the people around you, and without any formal mentoring process, they start picking things up simply by working alongside you.

You have a solid, intuitive understanding of hot-path optimization, speculative execution, and lazy initialization, and you’re occasionally surprised that these simple concepts aren’t more widely understood.

And the homelab experiments you keep running at home, purely because you’re curious and can’t help yourself? We definitely want to hear about those.

If reading this feels a little too familiar, this role is likely to be a very good fit.

What will you be doing?

• Manage your own time while adhering to priorities set by the company.
• Own complex engineering problems end-to-end, from problem framing and design through to delivery and iteration.
• Take responsibility for critical areas of the platform, ensuring they remain reliable, performant, and maintainable.
• Build new features and improve existing ones across our platforms.
• Refactor legacy and modern codebases pragmatically, balancing long-term health with delivery needs.
• Write tests (unit, integration, and end-to-end) to ensure software reliability.
• Be involved in every phase of the software lifecycle, from ideation to deployment.
• Participate in (and at times lead) deep technical discussions, helping drive sound decisions and trade-offs.
• Work hands-on across backend and frontend systems, stepping in wherever the problem lives.
• Identify inefficiencies and help streamline workflows, reducing unnecessary work.
• Collaborate closely with other senior engineers, raising the bar through example rather than authority.
• Take ownership of your work, ensuring high-quality results and maintainable solutions.

What will you bring along?

• 15+ years hands-on experience building and maintaining complex web applications.
• Clear technical communication; able to explain and defend design decisions to senior engineers and non-engineers alike.
• Expert PHP developer (12+ years); Symfony or equivalent frameworks.
• 10+ years modern JavaScript; React or Vue (Next/Nuxt a plus).
• Expert level knowledge in at least one more programming language (Python a plus).
• Full-stack architecture expertise: monoliths, services, and hybrids.
• Power user cloud deployment and scaling (AWS preferred) experience and abilities.
• Expert Linux user; including daily containerized workflows with Docker.
• Expert in infrastructure automation: Terraform, Ansible.
• Power user level CI/CD pipeline and release workflow ownership.
• Experience in automated testing: unit, integration, E2E; TDD where appropriate.
• Expert level knowledge in and around web security fundamentals: auth, authorization, data protection, secure coding.
• Legacy + modern codebase fluency; ability to work on incremental modernization.
• Strong independent technical ownership and accountability.

We are always looking for the best candidates, so if you think you would be a good fit even if you don't meet 100% of the requirements, we would love to hear from you!

How We Support Our Contractors

• €85/hour + retention bonus scheme: Competitive contractor rate with a generous bonus paid every 6 months based on your time with us.
• Top-Notch Workstation: We provide the latest MacBook, branded merchandise, and everything you need for an optimal work environment.
• Global Co-Working Access: Work from a global network of co-working spaces to keep your work-life dynamic and flexible.
• Flexibility: Enjoy full flexibility in work location and hours, supporting a work-life balance tailored to your needs.
• Events and Gatherings: Participate in exciting events throughout the year, including team gatherings, cultural events, and other fun activities.