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- Tasks: Build and scale OnBuy’s core commerce platform across front-end and back-end systems.
- Company: Join one of the UK's fastest-growing tech companies on a mission to be the best online marketplace.
- Benefits: Competitive day rate, remote work, and a chance to make a real impact.
- Other info: UK remote role with excellent career growth opportunities in a dynamic environment.
- Why this job: Own end-to-end engineering delivery and shape customer experiences with cutting-edge technology.
- Qualifications: Strong full stack experience, PHP expertise, and modern JavaScript skills required.
Who are OnBuy? OnBuy are an online marketplace who are on a mission of being the best choice for every customer, everywhere. We have recently been named one of the UK's fastest-growing tech companies in the Sunday Times 100 Tech list. All achievements we are very proud of, but we don't let that go to our head. We are all laser focused on our mission and understand the huge joint effort ahead of us needed to succeed.
Working at OnBuy: This is a critical role responsible for building, scaling, and evolving OnBuy’s core commerce platform across both front‑end and back‑end systems. As a Senior Full Stack Engineer, you will own engineering delivery end‑to‑end; from customer‑facing experiences to underlying services and data systems. You will operate within a cross‑functional team and be accountable for shipping high‑quality, scalable solutions that directly impact GMV, seller performance, and customer experience. This role moves beyond “front‑end vs back‑end” you are an Engineer responsible for outcomes, not layers.
- End-to-End Engineering Ownership
- Design, build, and maintain full‑stack solutions across UI, APIs, and backend systems
- Translate product requirements, designs, and wireframes into scalable, production‑ready systems
- Own features from concept → development → testing → release → monitoring
- Front‑End Excellence
- Build responsive, high‑performance user interfaces using modern JavaScript frameworks
- Translate UI/UX designs into clean, maintainable code
- Optimise applications for speed, scalability, and usability
- Back‑End & Platform Engineering
- Design and develop scalable services and APIs
- Work across monolith and microservices architecture (Laravel / PHP services)
- Maintain and evolve legacy systems while building modern, scalable architecture
- Quality & Engineering Standards
- Own quality to production — testing is embedded, not a phase
- Write and maintain automated tests (unit, integration, end‑to‑end)
- Participate in and lead code reviews to ensure high engineering standards
- Debug, troubleshoot, and resolve issues across the stack
- Performance & Scalability
- Optimise systems for performance, reliability, and scale
- Work with large‑scale data systems (MySQL, NoSQL, search platforms)
- Identify bottlenecks and proactively improve system efficiency
- Collaboration & Leadership
- Work in cross‑functional teams with Product, Design, QA, and other Engineers
- Mentor and support less experienced engineers
- Communicate technical concepts clearly to non‑technical stakeholders
Essential
- Strong full stack engineering experience, owning end‑to‑end delivery
- Proven backend expertise in PHP (Laravel)
- Strong JavaScript (ES6+) skills with modern frameworks (React/Vue/Angular)
- Experience designing and building RESTful APIs and scalable systems
- Experience with MySQL and NoSQL databases (e.g. Couchbase, MongoDB)
- Strong understanding of system architecture and microservices
- Experience with event‑driven systems (e.g. RabbitMQ, Pub/Sub) and cloud environments (GCP)
- Familiarity with Docker and CI/CD pipelines
- Strong engineering practices: testing, code quality, and production ownership
Desirable
- Experience in eCommerce or marketplace platforms
- Cloud experience (GCP)
- Experience with NoSQL (e.g. Couchbase) and Search platforms (e.g. Constructor & Solr)
- Experience working in microservices architecture
This role is UK remote role you must be based in the UK and have full right to work in the UK. The day rate is ÂŁ550-ÂŁ650 per day. Please confirm your outside IR35 day rate upon application. This is a 4 month contract.
Our Commitment
OnBuy is an equal opportunities employer. We are dedicated to creating a fair and transparent workforce, starting with a recruitment process that does not discriminate on the basis of gender, sexual orientation, marital or civil partnership status, pregnancy or maternity, gender reassignment, race, colour, nationality, ethnic or national origin, religion or belief, disability, or age.
Senior Full Stack Engineer Contractor employer: OnBuy
Contact Detail:
OnBuy Recruiting Team
StudySmarter Expert Advice 🤫
We think this is how you could land Senior Full Stack Engineer Contractor
✨Tip Number 1
Network like a pro! Reach out to your connections in the tech industry, especially those who work at OnBuy or similar companies. A friendly chat can lead to valuable insights and even referrals that could get your foot in the door.
✨Tip Number 2
Show off your skills! Create a portfolio showcasing your best projects, especially those that highlight your full stack capabilities. Make sure to include links to your GitHub or any live demos to impress potential employers.
✨Tip Number 3
Prepare for the interview! Research OnBuy’s mission and values, and think about how your experience aligns with their goals. Be ready to discuss your past projects and how you’ve tackled challenges in full stack development.
✨Tip Number 4
Apply through our website! It’s the best way to ensure your application gets seen by the right people. Plus, it shows you’re genuinely interested in joining the OnBuy team and contributing to their exciting journey.
We think you need these skills to ace Senior Full Stack Engineer Contractor
Some tips for your application 🫡
Show Off Your Skills: When you're writing your application, make sure to highlight your full stack engineering experience. We want to see how you've owned end-to-end delivery in your past roles, so don't hold back on the details!
Tailor Your Application: Take a moment to customise your application for us at OnBuy. Mention specific technologies like PHP (Laravel) and modern JavaScript frameworks that you’ve worked with. This shows us you’re not just sending out a generic application.
Be Clear and Concise: Keep your application straightforward and to the point. We appreciate clarity, so make sure your experience and skills are easy to read and understand. Avoid jargon unless it’s relevant to the role!
Apply Through Our Website: We encourage you to apply directly through our website. It’s the best way for us to receive your application and ensures you don’t miss any important updates from our team!
How to prepare for a job interview at OnBuy
✨Know Your Tech Stack
Make sure you’re well-versed in the technologies mentioned in the job description, especially PHP (Laravel) and modern JavaScript frameworks like React or Vue. Brush up on your knowledge of RESTful APIs and database systems like MySQL and NoSQL, as these will likely come up during technical discussions.
✨Showcase Your End-to-End Experience
Prepare to discuss specific projects where you’ve owned the entire engineering delivery process. Be ready to explain how you translated product requirements into scalable solutions and the impact your work had on user experience and system performance.
✨Demonstrate Collaboration Skills
Since this role involves working in cross-functional teams, think of examples where you’ve successfully collaborated with product managers, designers, and other engineers. Highlight your ability to communicate complex technical concepts to non-technical stakeholders, as this is crucial for the role.
✨Prepare for Problem-Solving Questions
Expect to face questions that test your problem-solving skills, particularly around debugging and optimising systems. Practice explaining your thought process when identifying bottlenecks and improving system efficiency, as this will showcase your analytical abilities and engineering mindset.