Senior Full Stack Engineer Contractor
Remote | United Kingdom | Technology | Contract
Description
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
Requirements
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
Work Arrangement
Remote — UK-based role. You must be based in the UK and have full right to work in the UK.
Compensation
Day Rate: £550-£650 per day (outside IR35)
Contract Duration: 4 months
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