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

Date Posted: 2026-02-27Country: United States of AmericaLocation: US-CA-REMOTEPosition Role Type: RemoteU.S. Citizen, U.S. Person, or Immigration Status Requirements: Active and transferable U.S. government issued security clearance is required prior to start date.​ U.S. citizenship is required, as only U.S. citizens are eligible for a security clearance​Security Clearance Type: DoD Clearance: TS/SCISecurity Clearance Status: Active and existing security clearance required on day 1 RTX Corporation is an Aerospace and Defense company that provides advanced systems and services for commercial, military and government customers worldwide. It comprises three industry-leading businesses – Collins Aerospace Systems, Pratt & Whitney, and Raytheon. Its 185,000 employees enable the company to operate at the edge of known science as they imagine and deliver solutions that push the boundaries in quantum physics, electric propulsion, directed energy, hypersonics, avionics and cybersecurity. The company, formed in 2020 through the combination of Raytheon Company and the United Technologies Corporation aerospace businesses, is headquartered in Arlington, VA. RTX BBN Technologies, a subsidiary of RTX Corporation, is the research company behind many revolutionary advances that we take for granted today. BBN is where email was invented and the first routers were implemented. Today, BBN's scientists and engineers are working to advance the state-of-the-art on topics ranging from machine language translation to quantum cryptography. BBN offers the opportunity to perform exciting and revolutionary research that solves important problems in an exciting, collaborative environment. Come join our team to develop the tools for the technology-augmented warfighter of the future! Front-line operators in the military, law enforcement, search and rescue teams, and other areas increasingly rely on cutting-edge technologies to give them an edge in terms of planning, decision-making, and communication. We are looking for people to join us in developing artificial intelligence and machine learning based solutions, tactical battlefield situational awareness applications, and cybersecurity technologies. As part of our team, you will be developing initial prototype technologies and transitioning these technologies to operational use. What You Will Do - Responsibilities include, but are not limited to: - Work with a small team on cutting-edge research and development projects - Design and develop prototype software using the latest open-source technologies - Receive and incorporate feedback from end users, field tests, and exercises - Explore technical possibilities collaboratively with motivated, world class colleagues - Deliver practical solutions to complex problems - Provide On-Site support to customer environments in San Diego, CA Qualifications You Must Have - BS degree in Computer Science, Computer Engineering, Electrical Engineering, or relevant field plus 5 years of related experience, or MS plus 3 years’ experience, or PhD graduate - Significant experience with Java, Linux, Computer Networking, and Cloud Integration - Experience with distributed systems, cybersecurity, middleware - Creative problem solving and experimental design - Good oral and written communication skills - Work in a self-directed manner as part of a team - Willing to travel 10% to 15% - Active and transferable U.S. government issued TS/SCI security clearance is required prior to start date.​ U.S. citizenship is required, as only U.S. citizens are eligible for a security clearance What We Offer Whether you’re just starting out on your career journey or are an experienced professional, we offer a robust total rewards package with compensation; healthcare, wellness, retirement, and work/life benefits; career development and recognition programs. Some of the benefits we offer include parental (including paternal) leave, flexible work schedules, achievement awards, educational assistance and child/adult backup care. • This position fully remote with upward of 15% travel To help you achieve your goals, BBN will provide: - A strong leadership team well-versed in government R&D. - A collaborative and collegial environment to push state-of-the-art research. - Technically competent pool of research scientists who are willing to mentor, listen, and help you refine your research vision and goals. - Business development, programmatic, contracting, finance, and HR support. - Access, through RTX, to opportunities that help transition your research and ultimately see it fielded. As part of our commitment to maintaining a secure hiring process, candidates may be asked to attend select steps of the interview process in-person at one of our office locations, regardless of whether the role is designated as on-site, hybrid or remote. The salary range for this role is 86,800 USD - 165,200 USD. The salary range provided is a good faith estimate representative of all experience levels. RTX considers several factors when extending an offer, including but not limited to, the role, function and associated responsibilities, a candidate’s work experience, location, education/training, and key skills. Hired applicants may be eligible for benefits, including but not limited to, medical, dental, vision, life insurance, short-term disability, long-term disability, 401(k) match, flexible spending accounts, flexible work schedules, employee assistance program, Employee Scholar Program, parental leave, paid time off, and holidays. Specific benefits are dependent upon the specific business unit as well as whether or not the position is covered by a collective-bargaining agreement. Hired applicants may be eligible for annual short-term and/or long-term incentive compensation programs depending on the level of the position and whether or not it is covered by a collective-bargaining agreement. Payments under these annual programs are not guaranteed and are dependent upon a variety of factors including, but not limited to, individual performance, business unit performance, and/or the company’s performance. This role is a U.S.-based role. If the successful candidate resides in a U.S. territory, the appropriate pay structure and benefits will apply. RTX anticipates the application window closing approximately 40 days from the date the notice was posted. However, factors such as candidate flow and business necessity may require RTX to shorten or extend the application window. RTX is an Equal Opportunity Employer. All qualified applicants will receive consideration for employment without regard to race, color, religion, sex, sexual orientation, gender identity, national origin, age, disability or veteran status, or any other applicable state or federal protected class. RTX provides affirmative action in employment for qualified Individuals with a Disability and Protected Veterans in compliance with Section 503 of the Rehabilitation Act and the Vietnam Era Veterans’ Readjustment Assistance Act. Privacy Policy and Terms: Click on this link to read the Policy and Terms