Senior Full Stack Engineer

Junior AI; Greater London; On-site; GBP 130,000 - 150,000; Full time

Benefits offered by this job

Private health insurance

Third Space gym membership

Dinner provided when working late

Team lunch provided every day at the  

Frequent international off-sites, Cré

Job summary

Junior is building an AI operating system for investment research. You will own features end to end across the frontend, backend and data layers, shipping on a weekly cadence and working closely with paying customers in London.

You’ll be a strong engineer with 5+ years, deep TS/Next.js and PostgreSQL expertise, and the ability to ship polished React interfaces while maintaining a client-facing mindset.

Qualifications

• 5+ years of engineering experience.
• Strong in TypeScript, Next.js and PostgreSQL.
• Able to design and ship polished React/Next.js interfaces.
• Solid foundations in data structures, system design and PostgreSQL.
• High-agency, product-minded with end-to-end ownership.
• Willing to work in London in person.

Responsibilities

• Own features end to end across frontend, backend and data layer.
• Ship on a weekly cadence.
• Design and build new ways of working with computers.
• Work on AI-powered projects and LLMS.
• Speak directly with clients using what you build and shape product decisions.

Skills

5+ years engineering experience

high-agency/product-minded

owns projects end to end

client-facing

clear communicator

Tools

TypeScript

Next.js

PostgreSQL

React

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!

Compensation: £130K – £150K Offers Equity

• Senior Base Salary £130K – £150K Offers Equity