Founding Software Engineer

What Stackfix does

We help businesses cut costs and grow revenue with tailored AI. A factory processes orders by hand. A distributor loses deals because quotes take days. A fleet team copies information between systems.

We combine AI agents, proven software modules and custom development to reduce manual work, win more business and improve margins.

About us

Paddy worked at Google and founded Jukedeck, a neural-networks-for-music company acquired by TikTok. Tom founded and sold an HR software company in 2023 and has more than nine years of experience building AI systems.

We are backed by Seedcamp, Chalfen Ventures, TSIC and helloworld, with angel investors including Matt Clifford and Alice Bentinck, co-founders of Entrepreneur First, and engineers from DeepMind.

The role

You will own AI builds end-to-end for specific clients.

• Sit with operators on-site and map how the work is done.
• Build and ship working software.
• Integrate with whatever the client already runs.
• Own the system after it goes live.

A typical project starts with customer discovery in week one, a working prototype handling the first high-volume cases by week four, and a system processing real transactions every day by week twelve. Projects usually run for four to nine months.

You will write code, ship systems, work with customers and upgrade the system over time.

What you will build

• LLM-based document processing.
• Extraction, classification, review and decision workflows.
• Human-in-the-loop review flows.
• Evals and regression testing for AI behaviour.
• Data quality checks and failure-mode handling.
• Observability, audit trails, permissions and production support.
• Python backends. Our default is Django.
• Integrations with CRMs, ERPs, case management systems, email, spreadsheets, databases and legacy software.

We build AI systems reliable enough that operators use them every day.

Tech stack

We use boring software wherever possible to minimise complexity. The stack varies per customer; our default is Python, Django, HTMX, Alpine.js, TypeScript and Postgres.

• Python
• Django
• HTMX
• Alpine.js
• TypeScript
• Postgres

Who this role is for

The systems you have built matter more to us than your job titles. You should apply if:

• You have 5+ years building production software.
• You are strong in a common language such as Python or TypeScript.
• You like talking to users.
• You can reason clearly about reliability, evals, data quality and edge cases.
• You care whether software creates measurable value.

We also look for evidence of sustained excellence. That could be engineering, sport, music, research, open source, a previous company or something else. What matters is the pattern: high standards, a long attention span and visible output.

How we work

This is an in-person role for someone who enjoys understanding how a customer makes money and taking responsibility across the whole product. It will not suit someone looking for remote work, minimal customer contact, or a narrow backend or frontend role.

We optimise for autonomy, quality and sustained output rather than long hours.

What you get

• Ownership: own client builds from discovery to production.
• Commercial exposure: see how companies make money, where they lose margin and where software creates value.
• Founder-level learning: work directly with two exited founders and see how we sell, scope, negotiate, build, hire and run the company.
• Commission: on new customers you bring.
• Tools and workspace: a new MacBook Pro, subscriptions to the AI models you need, and a central private office in Holborn.

Hiring process

1. 01

   Intro call

   Up to 30 minutes

   A conversation about your background, what you are looking for and the role.

2. 02

   Technical screen

   Up to 30 minutes

   A focused discussion of how you approach engineering problems.

3. 03

   On-site technical interview

   Up to 2 hours, plus a team conversation

   A practical engineering discussion based on the work we do.

4. 04

   Paid work afternoon and lunch

   In person · 4 hours · Paid

   Work with us in Holborn and get a feel for the role and the team.

Right to work

You must have the right to work in the UK. We do not sponsor visas.