Senior Full Stack Engineer CONTRACTOR - from until

On Commerce is a global selling platform that powers a growing network of retail channels, including:

• On Buy - The only marketplace in the world to give customers instant Cashback on everything
• easyShop - An all-new marketplace created in collaboration with the easy® family of brands
• Comet - The iconic UK tech brand making its return later this year

On Commerce is growing fast, launching new brands and scaling to power the future of ecommerce.

On Commerce is constantly evolving. Everyone here plays a hands‑on role in shaping what comes next, building brands that make an impact across global markets. There’s no red tape or rigid corporate structure; just smart people taking ownership and figuring things out as we build something big together. The pace is fast, priorities shift, things aren’t always perfectly set up, and you’ll often need to get stuck in and solve problems.

But if you thrive in that kind of environment, you’ll have real influence, real ownership, and the chance to grow with a rapidly scaling business.

• Design, build, and maintain full‑stack solutions across UI, APIs, and backend systems
• Translate product requirements, designs, and wireframes into scalable, production‑ready systems
• Optimise applications for speed, scalability, and usability

• 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

• 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

• Optimise systems for performance, reliability, and scale
• Work with large‑scale data systems (MySQL, No
  
  SQL, search platforms)
• Identify bottlenecks and proactively improve system efficiency
• 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

• Strong full stack engineering experience, owning end‑to‑end delivery
• Experience designing and building RESTful APIs and scalable systems
• Experience with MySQL and No
  
  SQL 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
• Experience in eCommerce or marketplace platforms
• Cloud experience (GCP)
• Experience with No
  
  SQL (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 £450-£600 per day. Please confirm your outside IR35 day rate upon application. This is a contract role until the end of August 2026.

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.