Full Stack Developer

Position Overview

We are looking for a Full Stack Developer to build and extend the InSync Excel Add-in. For most of our clients, Excel is not one channel among many. It is where the work actually happens. Analysts build models there, and our add-in is what puts live estimates, actuals, and guidance directly into their cells. This role is for someone who wants to go deep on a hard, specific surface rather than build another CRUD application.

About the Role

You will own the client-side product that sits inside Excel: task panes, ribbon commands, and custom functions built on the Office JavaScript API, backed by Python services you also build. The frontend is TypeScript; the backend is Python; the constraint is Excel itself.

That constraint is what makes the role interesting. A workbook may hold tens of thousands of InSync formulas that all need to resolve without freezing the application. Recalculation, calc chains, volatile functions, undo behaviour, and error propagation all become your problem. An analyst's model is their working capital, and breaking it is not an acceptable failure mode.

Requirements

• 1 to 3 years of relevant experience as a Full Stack Developer, Python Developer, or in a similar role.
• Strong TypeScript and JavaScript, with solid HTML5 and CSS3.
• Hands-on experience building Microsoft Office add-ins with Office.js, or adjacent experience (VSTO, COM add-ins, XLL, RTD servers, Google Apps Script, or VBA at scale) plus a real appetite to specialise here.
• Strong hands-on experience with at least one Python framework: FastAPI, Django, or Flask.
• Solid understanding of RESTful API design and development.
• Experience with SQL databases (PostgreSQL, MySQL) and Redis.
• Proficiency with Docker and experience deploying containerised applications.
• Understanding of web security fundamentals: authentication, authorisation, and common OWASP risks.
• Experience with Git and agile development.
• Comfort with complex business logic and real-world datasets; strong problem-solving and attention to detail.

Good to Have

• Experience with spreadsheet automation beyond Office.js, such as openpyxl, xlwings, or building against the Excel object model.
• Familiarity with financial modelling conventions or having built tooling used by analysts.
• Experience publishing to AppSource or managing centralised Microsoft 365 deployments.
• Automated testing frameworks (PyTest, Jest, Playwright, or similar).
• Cloud experience: AWS, Azure, or Google Cloud.
• AI/ML or Generative AI interest.