Senior Backend Engineer (Ruby)

Senior Backend Engineer (Ruby)

London | Hybrid

Who are Zuno?
Zuno is the tech platform behind BOXT. We manage the whole installation process for home energy products, from boilers and air conditioning to heat pumps, solar, batteries and EV chargers. We work with brands like E.ON Next, EDF Energy, Worcester Bosch and Tesla to get their products into customers’ homes.
Millions of people visit every year for a fixed-price quote. We’ve installed over 200,000 products so far and built a network of more than 15,000 accredited installers.
We built the tech ourselves, and it covers everything from quoting and buying to matching installers with jobs, scheduling visits and aftercare. The aim is simple: make getting a new heat pump or boiler as easy as ordering anything else online.
We’re backed by Brookfield and growing fast as more UK homes move to cleaner energy. There’s a lot still to build.
The role

As a Senior Backend Engineer, you will be acting as a technical anchor within the team, defining the architectural direction of our server-side logic and ensuring the scalability of our data models. You will partner with Product Managers to shape the roadmap and ensure technical feasibility from the outset. In this role, you will be responsible for designing and optimising high-performance APIs and complex business logic using Ruby on Rails. While your focus is backend, you will work closely with frontend engineers to define API contracts and ensure seamless integration with our Next.js frontend.
You'll also contribute to keeping the quality of the code top-notch by reviewing your teammates' code and mentoring junior engineers.

Key responsibilities

• Core Backend Architecture: Design, build, and maintain robust, scalable, and secure backend features using Ruby on Rails, ensuring business logic is encapsulated and efficient

• API Strategy: Architect and document performant RESTful APIs, acting as the bridge between server-side logic and the React/Next.js frontend teams

• Technical Leadership: Lead technical discussions on system design, database schema planning, and the decoupling of monolithic services where necessary

• Performance & Scalability: Proactively identify and resolve performance bottlenecks, focusing on SQL query optimisation, caching strategies (Redis), and background job management (Sidekiq/Solid Queue)

• High-Quality Engineering: Write clean, maintainable, and efficient code that adheres to best practices (including Test-Driven Development and Continuous Delivery)

• Feature Ownership: Take ownership of complex backend features from concept to deployment; assisting the Product Team in scoping requirements and managing technical debt

• Driving Engineering Culture: Act as a catalyst for technical excellence by evolving our backend engineering standards (OOAD, SOLID principles) and internal processes. You will proactively identify and resolve bottlenecks, whether in code, deployment, or communication, advocating for the changes needed to make the backend team faster, safer, and more efficient.

• Mentorship: Actively mentor junior and mid-level engineers, fostering a culture of continuous learning and technical excellence

• System Reliability: Debug and resolve complex issues in production, ensuring high availability and data integrity for our installer and customer platforms

• Continuous Improvement: Stay up-to-date with the Ruby on Rails ecosystem and emerging backend technologies, bringing fresh ideas to the team to improve our infrastructure

Skills

• 5+ years of professional experience in backend development

• Deep expertise in Ruby and the Ruby on Rails framework, including a strong understanding of metaprogramming and the Rails internal architecture

• Proven ability to design complex, normalised database schemas and write performant SQL (PostgreSQL focus), with a keen eye for avoiding and resolving N+1 queries and lock contention

• A firm grasp of Object-Oriented Analysis and Design (OOAD), design patterns, and software engineering best practices

• Experience designing and maintaining versioned, documented RESTful APIs

• Experience writing comprehensive automated tests using RSpec, including integration and request specs

• Experience working within Agile development methodologies

• Proficiency with version control systems, particularly Git, and modern workflows (Pull Requests, Code Reviews)

• Strong problem-solving skills, with a focus on writing simple, clean, and efficient code

• Natural tendency to identify internal pain points and the initiative to propose and implement technical or procedural improvements

• Excellent communication skills, with the ability to explain complex backend concepts to frontend developers and non-technical stakeholders

Beneficial skills/interests but not essential

• Advanced DevOps experience (Infrastructure as Code, AWS, Kubernetes, Docker)

• Experience with React and Next.js (ability to read frontend code to understand how it consumes your APIs)

• Experience with TypeScript

• Knowledge of Site Reliability Engineering (SRE) practices and monitoring tools (New Relic)

• Experience scaling applications using background processing tools (Sidekiq)

Benefits

• 30 days annual leave + bank holidays!

• Private medical cover with Aviva*

• 4 x salary Death in Service cover with Zurich*

• Paid 6 months maternity pay after a year of service

• Paid paternity pay after a year of service

• £1000 annual training budget*

• Salary sacrifice pension matched up to 6%

• Flexible working times and location

• Company MacBook Pro & accessories

• Team lunches, team events

*After probationary period

Please note: We’re unable to offer visa sponsorship for this role, so candidates must already have the right to work in the UK.