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: We are a team of driven and motivated people who thrive when working at pace. To succeed at OnBuy you need to take charge and fully own your responsibilities, rolling your sleeves up when needed to 'get it done'. Working at OnBuy you are surrounded by so much opportunity, but you must possess the ability to stay focused and prioritise ruthlessly. Most importantly, you will thrive in an ever-changing environment as we are constantly evolving. At OnBuy, you're not just a number or another cog in a machine. We are creating something really special, and you have the opportunity to affect meaningful change and have your voice heard. We are a close team, who have the opportunity to learn and grow as OnBuy evolves. 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

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: We are a team of driven and motivated people who thrive when working at pace. To succeed at OnBuy you need to take charge and fully own your responsibilities, rolling your sleeves up when needed to 'get it done'. Working at OnBuy you are surrounded by so much opportunity, but you must possess the ability to stay focused and prioritise ruthlessly. Most importantly, you will thrive in an ever-changing environment as we are constantly evolving. At OnBuy, you're not just a number or another cog in a machine. We are creating something really special, and you have the opportunity to affect meaningful change and have your voice heard. We are a close team, who have the opportunity to learn and grow as OnBuy evolves. 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

• Play a critical role in growing and evolving the app as the 5th engineer. • Work with high autonomy and speed, involved in the end-to-end product development cycle. • Significant input into norms and tools for high performing engineering team. • Work cross-functionally with product designers, creative designers, character animators, and founders. • Be a thought partner in building a product, company, and culture we are proud of.

• Build product - working closely with design and product to plan, architect, and implement core product • Build our technical foundation - establish a flexible foundation for future work • Grow the team - attract, close, and grow other talented team members • Developing AI features to assist customer understanding • Best in-class data visualization and analysis tools