Senior Full Stack Engineer

Junior AI; Greater London; On-site; GBP 90,000 - 140,000; Full time

Benefits offered by this job

Private health insurance

Team lunches

International off-sites

Gym membership

Dinners provided when working late

Job summary

Junior in London is seeking a senior software engineer to own features end to end across the frontend, backend and data layer, shipping on a weekly cadence and speaking directly with paying customers.

You’ll be deeply hands-on with TypeScript, Next.js and PostgreSQL, able to design polished React/Next.js interfaces, tackle hard TS problems live, and help shape Junior’s engineering culture as the team grows in Farringdon. 5+ years of experience required; London-based or relocating to Farringdon.

Qualifications

• 5+ years of engineering experience
• Strong in TypeScript, Next.js and PostgreSQL
• Able to design polished React/Next.js interfaces
• Can solve difficult TypeScript problems live
• High-agency and product-minded

Responsibilities

• Own features end to end across frontend, backend and data layer
• Ship on a weekly cadence
• Speak directly with clients using what you build
• Use conversations to shape product decisions
• Help define Junior’s engineering culture as the team grows

Skills

TypeScript

Next.js

PostgreSQL

React

System design

End-to-end ownership

Client-facing

Job description

About Junior

Junior is building the AI operating system for investment research. Our software helps private equity firms, consultants and financial institutions complete high-stakes research workflows dramatically faster - from diligence and memo writing to market mapping, research synthesis and strategic analysis.

We’re trusted by several of the world’s top private equity firms, Big Four consultancies and leading financial institutions.

• Bootstrapped and profitable

• ~£20M+ in revenue, after growing 10x last year

• 60+ people across the company

• 20-person engineering team, doubling to 40 this year

• Core stack: TypeScript, Next.js and PostgreSQL

You’d be joining early enough to shape the product, engineering culture and company, but with enough traction that everything you build lands immediately in front of demanding, paying customers.

The role

You’ll own features end to end - across the frontend, backend and data layer - and ship on a weekly cadence, not a quarterly one.

You’ll:

• Ship quickly, then ship again

• Design and build entirely new ways of working with computers

• Work on groundbreaking projects involving LLMs

• Speak directly with the clients using what you build

• Use those conversations to shape product decisions

• Help define Junior’s engineering culture as the team doubles

Sample projects

• Build frontier products capable of ingesting new types of research inputs

• Build an extremely low-latency, voice-to-voice survey tool that autonomously conducts high volumes of research

• Build a mobile app from scratch in three weeks

• Create segmented knowledge graphs using unstructured-to-structured data transformations

• Build an AI-native CRM with deep links into that knowledge graph

About you

• You have 5+ years of engineering experience - we care about demonstrated competence, not pedigree

• You’re genuinely strong in TypeScript, Next.js and PostgreSQL, not merely familiar with them

• You can build a polished React/Next.js interface or work through a difficult TypeScript problem live and quickly, without relying on Copilot

• You have solid foundations in data structures, system design and PostgreSQL

• You’re high-agency and product-minded

• You’ve owned projects end to end, argued for what should be built - not only how - and shipped without being handed a detailed specification

• You communicate clearly and want a client-facing role

• You’re based in London, or already committed to relocating, and excited to work with the team in person in Farringdon

• You feel like you’re never building fast enough

• Bonus: you’ve built and designed AI-powered products

Interview process

The process moves in days, not months:

1. Introductory call: background, motivation and mutual fit

2. Live technical screen (30-mins): solving a TypeScript problem live in an IDE with one of our engineers. We optimize for speed and completeness over polish, and the interview is completed without AI tools

3. On-site Interview: a full afternoon of coding, a system-design whiteboard and a product discussion with one of our PMs

4. Final Cultural Round: a final conversation about how you work, what motivates you and whether Junior is the right environment for you

5. Offer: decisions are made collectively and quickly

Benefits

• Private health insurance

• Third Space gym membership

• Dinner provided when working late

• Team lunch provided every day at the office

• Frequent international off-sites, recently including Crete and Cancún

If you’re excited to drive innovation at Junior, we’d love to hear from you!