Senior Full Stack Engineer

Junior
London, United Kingdom
On-site

Who this role is best for

Aimed at senior full stack engineers who can rapidly develop end-to-end features in a fast-paced environment.

Best fit for

  • Candidates with end-to-end project ownership experience and client-facing engineering skills
    — “You’ve owned projects end to end, argued for what should be built - not only how - and shipped without being handed a detailed specification
  • Experienced engineers with a track record in AI-powered product development
    — “Bonus: you’ve built and designed AI-powered products
  • Highly autonomous individuals who thrive in shaping engineering culture during rapid growth
    — “Help define Junior’s engineering culture as the team doubles

Things to consider

  • Requires in-person presence in London’s Farringdon office for team collaboration
    — “excited to work with the team in person in Farringdon
  • Technical interviews demand live problem-solving without AI assistance
    — “solving a TypeScript problem live in an IDE... without AI tools

How to stand out

  • Demonstrate live TypeScript problem-solving in your portfolio or interview prep
    — “work through a difficult TypeScript problem live and quickly, without relying on Copilot
  • Highlight experience with unstructured-to-structured data transformations in projects
    — “Create segmented knowledge graphs using unstructured-to-structured data transformations
  • Emphasize client-facing product decisions in your resume and interview stories
    — “Speak directly with the clients using what you build
Pace · Fast PacedCollaboration · HighAutonomy · HighDecision Impact · TeamLevel · Senior

Derived from job-description analysis by Serendipath's career intelligence engine.

What success looks like

  • ship features end to end
  • design and build entirely new ways of working with computers
  • work on groundbreaking projects involving LLMs
Typical background
5+ years of engineering experiencestrong foundations in data structures, system design and PostgreSQL

Skills & requirements

Required

TypeScriptNext.jsPostgreSQLReactSystem DesignData Structures

Preferred

LlmsAi-powered Products

Stack & domain

TypeScriptNext.jsPostgreSQLReactData StructuresSystem DesignCommunicationLeadershipFinance

About the role

Original posting from Junior via Ashby

👶 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:

  • Introductory call: background, motivation and mutual fit
  • 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
  • On-site Interview: a full afternoon of coding, a system-design whiteboard and a product discussion with one of our PMs
  • Final Cultural Round: a final conversation about how you work, what motivates you and whether Junior is the right environment for you
  • 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!

Source: Junior careers (Ashby)

Similar roles