Principal Software Engineer

We are building Lumen, our gas market intelligence and scenario modelling platform. It is in production with major energy and trading clients, and the next 12 to 18 months are about scaling it, hardening it, and pushing it past what our competitors are doing. We need a Principal Software Engineer to join us. This is a frontend‑leaning role, but it is not a frontend‑only role. We want someone who cares about how the product feels to use, who will push back on a design that is not working, and who can also reason about the data and infrastructure underneath it. You will report to the CTO and sit alongside our other principal engineers as a peer. You will lead our UI contractor team and work closely with the wider engineering and data teams. We are not looking for someone to come in and own everything. We are looking for someone who brings their own ideas and pulls their own weight, the way the rest of the senior team does.

What you will do:

• Own the frontend architecture for the products you work on: component structure, state, performance, the patterns your team follows.
• Lead our UI contractor team. Help set the bar for what we ship, review work, raise the quality.
• Push on UX. We are not looking for someone who builds whatever the design file says. We want someone who challenges it, prototypes alternatives, and argues for the user.
• Work with our data team on the contract between the UI and the data layer (Snowflake, Payload CMS, our scenario modelling backend).
• Bring R&D ideas. Prototype new patterns, try new tooling, contribute to where the product goes next.
• Hold your own on backend and platform decisions when it matters. You do not need to be the deepest backend person in the room, but you should be able to follow the conversation and add to it.

Job Requirements:

• Strong, current React 19 experience. Server components, the use hook, transitions, Suspense, and a clear view on where React is heading.
• Strong production Next.js experience. App Router, server actions, trade‑offs around SSR, static rendering, streaming and data fetching. You know when Next is worth its complexity and when it is not.
• Experience designing frontend architecture in production. Not just writing components, but deciding how a non‑trivial app is structured.
• Real opinions on state management. When to reach for what, and why most apps need less of it than people think.
• A working understanding of frontend performance. The actual reasons re‑renders happen, where bundle size hurts, and how to measure rather than guess.
• Engineering breadth, where this differs from a Senior FE role: Can model and structure data sensibly. Comfortable enough with databases to design schemes, reason about queries, and have a useful conversation with a data engineer.
• Working experience with cloud platforms: serverless, container‑based, or both. Does not need to be a platform engineer, but should know how production systems are deployed and run.
• A problem solver. Debugs systematically, asks good questions, and is not precious about which layer of the stack the answer lives in.
• A collaborator and sparring partner, not a ticket‑closer.

Product and design instincts:

• Cares about user experience as a craft. Has pushed back on a design and made it better, with stories to tell.
• Can prototype quickly to test an idea, not just build the final thing.
• Can challenge product, design and engineering decisions with substance.

What this role is not:

• Not a pure frontend specialist who hands off the moment something touches the API or the database.
• Not a pixel‑pushing implementer who builds whatever the design file says without asking why.
• Not a hands‑off architect. We expect you in the codebase, regularly.
• Not a manager role. You will lead the contractor team, but the job is principal IC working as part of a peer group of senior engineers.

Job Benefits:

• Real influence on a product that already has customers and is growing.
• A small senior team that cares about the work.
• UK hybrid working with regular days in our Edinburgh or London offices.
• Competitive compensation and benefits.
• The backing of an established industry leader, with the freedom of a small product team.

Location and requirements:

• UK hybrid with regular days in Edinburgh or London. The exact pattern is flexible and something we will work out with the right person.
• We cannot offer visa sponsorship.
• We actively encourage applications from women and other under‑represented groups in tech.
• If you care about how software is built and used, and you want a role where your judgement actually counts, get in touch.