Full Stack Engineer

9fin; Greater London; Hybrid; GBP 75,000 - 115,000; Full time

Benefits offered by this job

Competitive salary

Pension

Private medical insurance

Sick leave

Life assurance

Season ticket loan

Cycle to work

Hybrid working

Work abroad for up to 3 months

Sabbatical after 5 years

Job summary

9fin is the AI platform powering global debt markets. A Backend/Full-stack engineer is sought to design systems, build APIs, and advance data processing within our Python stack (FastAPI/Flask) on a hybrid UK-based team.

You will develop backend services, contribute to a broad range of platforms and collaborate with cross-functional teams, including product and clients, to deliver new features and improve the codebase with automation and testing.

Qualifications

• Experience as a full-stack or backend-focused engineer in a product team.
• Ability to plan and reason about software within larger systems.
• Experience designing data flow from storage to API endpoints with validation.
• Proficiency with Python and web frameworks (FastAPI with typing and Pydantic).
• Experience building and consuming APIs, ideally in a service-oriented architecture.
• Working knowledge of SQL for relational data.
• Collaborative and proactive communicator with engineers and non-engineers.

Responsibilities

• Contribute to projects by helping design systems, build proof of concepts, and deliver new service functionality (APIs, data processing, automation).
• Develop and maintain backend services and web-application–hosted tools within the 9fin platform.
• Participate in code reviews and collaborate with peers on new ideas and technologies.
• Improve the codebase through automation, refactoring, and documentation.
• Work across financial data modelling, access-control logic, data capture, ML/AI integration, visualization, and automation.
• Collaborate with cross-functional teams including financial, legal, and editorial colleagues to explain technical concepts.
• Support rapid iteration with strong developer experience practices (preview environments, feature flags, non-production environments).

Skills

Backend engineering

Full-stack

API design

Data flow

Communication

Tools

Python

Flask

FastAPI

PostgreSQL

Docker

AWS

ECS

Job description

About 9fin

9fin is the AI platform powering global debt markets — the world’s largest asset class at over $145 trillion.

Debt markets are vast, global, and mission-critical, yet still run on fragmented data, PDFs, and manual workflows. 9fin replaces this broken infrastructure with a single platform that centralises proprietary credit data, deep analysis, and high-value workflows across global markets.

Today, 9fin powers teams at 300+ blue-chip institutions worldwide, including global banks, asset managers, private equity firms, law firms, and advisors. The business is scaling at exceptional speed, with rapid expansion in the US and best-in-class retention driven by deep workflow adoption.

We’re at a defining inflection point. With proven product-market fit and strong, global market pull, 9fin is accelerating toward becoming the category-defining platform for debt markets worldwide.

What you’ll work on

• As part of a cross-functional team, contribute to projects by helping design systems, building proof of concepts, and delivering new service functionality — including APIs, data processing, and automation — while collaborating closely with Product and Clients.

• Development and engineering primarily on backend services and web-application–hosted tools and systems within the 9fin platform.

• Play an impactful role within project teams as an individual contributor, participating in code reviews, collaborating with peers, and contributing ideas during research and experimentation with new technologies.

• Continually improve the 9fin codebase by taking opportunities to automate, refactor, and document where it’s most valuable.

• Work across a diverse set of web platforms, including financial data modelling, access-control business logic, environmental and emissions data capture, integration with ML/AI prediction services, data visualisation, and automation systems.

• Collaboration and teamwork: All projects are delivered by cross-functional teams that include domain expertise from 9fin’s financial, legal, and editorial colleagues. You’ll work closely with non-technical stakeholders and help explain technical concepts in a clear, accessible way to support effective team progress.

• Developer experience: You’ll work within a strong developer experience setup, including automated preview environments, feature flags, and well-maintained non-production environments, enabling rapid iteration and feedback.

Our Backend Stack

• Python is the dominant backend language used

• Flask & FastAPI

• Typing is used within our Python stack to power automated documentation and API definitions

• Relational Databases (PostgreSQL) at the heart of majority of services

• We have our own internal developer platform with standardised paved road approaches to infrastructure to bring your code into production as quickly as possible.

• We’re AWS for Cloud hosted services

• Heavy use of AWS lambda Serverless

• Docker (AWS ECS) for uniform development/deployment from dev to prod

Requirements

This role will be a great fit if you:

• Have experience working as a Full-Stack or Backend-leaning Engineer within a product team, contributing to system design discussions and delivering production software.

• Can plan and reason about software effectively, clearly communicating how your work fits into larger systems and delivers value to clients.

• Have hands‑on experience designing and implementing data flow through software, from persistent storage to API endpoints, applying industry best practices for validation and reliability.

• Have experience with Python and web frameworks (we currently use FastAPI with strong typing and Pydantic).

• Have experience building and consuming APIs, ideally within a service-oriented architecture.

• Have a working knowledge of SQL for querying and working with relational data.

• Are a collaborative and proactive communicator, comfortable working with engineers and non-engineers across the business.

• Care about code quality, writing testable and maintainable code, and actively participating in code reviews — both receiving feedback and reviewing others’ work.

Benefits

We’re a scaling start up and we enjoy sharing our success, when the company succeeds, we always reinvest that in our people. We also offer huge amounts of responsibility, an abundance of opportunity for growth and a platform to truly excel.

Financial & Insurance

• Competitive Salary (our salary bands are benchmarked at the top end of the market)

• Pension (your minimum contributions are 4% with 9fin matching up to 7%)

• Private Medical Insurance

• Paid sick leave with Income Protection for long periods of illness

• Group Life Assurance

• Season Ticket Loan & Cycle to Work schemes

Time off

• 25 holiday days per year

• Local public holidays (with the ability to exchange them for alternative days)

• Hybrid working model, to allow you the flexibility to decide how, where and when you do your best work

• Work abroad for up to 3 months a year

• 1 month paid sabbatical after 5 years of service

• Enhanced parental leave & flexible working arrangements available

Training & Culture

• Professional learning and development budget

• Quarterly team socials

• Summer and Winter company social events

9fin is an equal opportunities employer

At 9fin we are dedicated to building and promoting a fair and inclusive workplace where everyone can reach their full potential and truly belong. We recognize that building diverse teams enables a more creative and productive environment. If you’re excited about this role but your experience doesn’t perfectly align with the job description, we encourage you to apply anyway. You might just be who we’re looking for — either for this role, or perhaps another.