At a Glance
- Tasks: Build innovative user-facing products that integrate advanced AI capabilities for developers.
- Company: Join Cosine, a cutting-edge tech company revolutionising software development with AI.
- Benefits: Enjoy competitive salary, equity options, 30 days holiday, and a dog-friendly office.
- Other info: Collaborative environment focused on work-life balance and professional growth.
- Why this job: Make a real impact by creating tools that enhance developer workflows and experiences.
- Qualifications: 5+ years in software development, strong frontend skills, and a passion for user experience.
The predicted salary is between 70000 - 90000 £ per year.
Location: London; full in-office working as default
Start date: ASAP
Reports to: Head of Engineering
Compensation: BASE: £70,000 - £90,000 EQUITY: £70,000 - £90,000
At Cosine, we’re building autonomous AI engineers that plan, write, and ship code inside real development workflows. Cosine is designed for on‑premise and virtual private cloud (VPC) deployments, including fully air‑gapped environments. We build our agent tooling entirely in‑house and post‑train open‑source models to deliver reliable, enterprise‑grade coding performance in security‑critical settings. In 2024, Cosine achieved a 72% score on OpenAI’s SWE‑Lancer benchmark, placing us among the strongest real‑world software‑engineering AI systems evaluated. YC‑backed and well‑funded, Cosine was founded by experienced operators focused on building dependable, production‑grade AI.
This role is based in our Hoxton office, five days a week, because close collaboration, fast feedback, and shared context matter for the problems we’re solving.
A Product Engineer at Cosine works closely across research, engineering, product, and design to turn advanced AI capabilities into intuitive, reliable tools for developers. You will be responsible for building and evolving Cosine’s user‑facing product surfaces, including IDE extensions or dedicated apps and web applications that expose the power of our models through well‑designed workflows and interfaces. Your work sits at the intersection of product, platform, and research, translating emerging model capabilities into concrete experiences developers can use every day. We focus on rapid product iteration without compromising quality. This means building systems that are performant, observable, and robust, while remaining flexible enough to evolve alongside fast‑moving research and user needs. You will help define how developers interact with Cosine, from first use through advanced, production‑grade workflows.
Responsibilities
- Build end‑user products (editor extensions and web applications and platform capabilities) that integrate with the Cosine platform APIs
- Enable developers to use advanced language models to augment their workflows and problem‑solving capabilities
- Collaborate closely with research to explore and validate new product experiences and capabilities
- Translate emerging model capabilities into concrete, user‑facing features
- Maintain a high bar for performance, reliability, and usability across platforms
- Be opinionated about and bring your own ideas to the table, we’re building for engineers, as an engineer you have a say in what you want to use.
Skills & Experience
Frontend & Application Development
- Experience building reactive, highly interactive applications (React, Svelte, Vue)
- Experience with CLI application development or local software development is a plus
Backend & Systems
- Comfortable with backend development
- Experience designing and consuming REST APIs
Developer Experience
- Experience working with developer tooling
- Familiarity with CI/CD pipelines
- Experience with containerization
Programming Languages
- Strong experience with TypeScript and modern frontend frameworks
- Knowledge of Node.js, Python, and Go is a plus
Tooling & Infrastructure
- Git, Docker, Webpack, npm
- Monitoring and alerting tools (e.g. Grafana, Datadog)
- Feature flagging systems
You Might Thrive in This Role If You:
- Have 5+ years of experience building production‑grade software, with a strong emphasis on user‑facing developer tools.
- Have shipped and maintained complex frontend or full‑stack applications used by technical users.
- Are comfortable building highly interactive web or IDE‑based experiences using modern frameworks (e.g. React, TypeScript).
- Have experience designing and consuming APIs, and understand how frontend and backend systems evolve together.
- Enjoy working close to the product surface, translating ambiguous ideas and model capabilities into intuitive developer workflows.
- Care deeply about developer experience, performance, and reliability—not just functionality.
- Are comfortable iterating quickly, running experiments, and refining products based on real user feedback.
- Can operate effectively in a fast‑moving environment with evolving priorities and incomplete information.
Cosine is an equal opportunity employer. We value diverse backgrounds, perspectives, and ways of thinking, and we’re committed to creating an inclusive and respectful workplace. We encourage applications from anyone who meets the role requirements, even if you don’t meet every single qualification. If you need reasonable adjustments at any stage of the hiring process, we’re happy to discuss them.
Compensation, Benefits & Ways of Working
We’re an in‑office team, five days a week, by design. We believe the work we’re doing benefits from being together, collaborating closely, and building shared context.
What you can expect:
- Competitive salary, benchmarked to the market
- Equity / share options, so you share in the upside you help create
- 30 days’ holiday + bank holidays
- Genuine 9–5 working hours – we don’t expect late nights or weekend work
- Work hard in the office, collaborate closely, and switch off properly
- Dog‑friendly office – bring your dog to work
- Weekly team breakfast & lunch
- Monthly socials
- Pension
- High‑quality equipment to do your best work
We care about focus, sustainability, and doing great work — not performative overwork. We value people who show up, contribute thoughtfully, collaborate well with their colleagues, and then go home. This role won’t suit everyone. But if you want structure, clarity, strong collaboration, and a team that takes both the work and work‑life balance seriously, it’s a great place to be.
Full Stack Product Engineer employer: Cosine
At Cosine, we pride ourselves on fostering a collaborative and inclusive work environment where innovation thrives. Our London-based team enjoys competitive salaries, equity options, and a genuine commitment to work-life balance, with 30 days of holiday and a dog-friendly office. We prioritise employee growth through close collaboration and rapid product iteration, making it an ideal place for those passionate about building impactful developer tools.
StudySmarter Expert Advice🤫
We think this is how you could land Full Stack Product Engineer
✨Tip Number 1
Network like a pro! Reach out to folks in your industry on LinkedIn or at meetups. A friendly chat can lead to opportunities that aren’t even advertised yet.
✨Tip Number 2
Show off your skills! Create a portfolio or GitHub repo showcasing your projects. This gives potential employers a taste of what you can do and how you think.
✨Tip Number 3
Prepare for interviews by practicing common questions and coding challenges. We recommend doing mock interviews with friends or using online platforms to get comfortable.
✨Tip Number 4
Don’t forget to apply through our website! It’s the best way to ensure your application gets seen. Plus, we love seeing candidates who are proactive about their job search.
We think you need these skills to ace Full Stack Product Engineer
Some tips for your application 🫡
Tailor Your CV:Make sure your CV reflects the skills and experiences that align with the Product Engineer role. Highlight your experience with frontend frameworks, backend development, and any relevant projects that showcase your ability to build user-facing tools.
Craft a Compelling Cover Letter:Use your cover letter to tell us why you're excited about working at Cosine. Share specific examples of how your past work has prepared you for this role and how you can contribute to our mission of building reliable AI tools for developers.
Showcase Your Projects:If you've worked on any interesting projects, especially those involving developer tools or interactive applications, make sure to include them in your application. We love seeing real-world examples of your work and how you approach problem-solving.
Apply Through Our Website:To ensure your application is considered, please apply through our website. This helps us keep everything organised and makes sure your details are processed correctly. Plus, it’s the best way to get your foot in the door with us!
How to prepare for a job interview at Cosine
✨Know Your Tech Stack
Make sure you’re well-versed in the technologies mentioned in the job description, like React, TypeScript, and REST APIs. Brush up on your knowledge of backend development too, as they’ll likely ask how frontend and backend systems work together.
✨Showcase Your Projects
Prepare to discuss specific projects where you've built user-facing developer tools or applications. Highlight your role, the challenges you faced, and how you overcame them. This will demonstrate your hands-on experience and problem-solving skills.
✨Emphasise Collaboration
Since the role involves working closely with research, engineering, and design teams, be ready to talk about your collaborative experiences. Share examples of how you’ve worked with cross-functional teams to turn ideas into reality.
✨Ask Insightful Questions
Prepare thoughtful questions about Cosine’s product vision and how they approach rapid iteration. This shows your genuine interest in the company and helps you assess if their work culture aligns with your values.
