Senior Full Stack Developer

Job Description

We are looking for a full-time Senior Full Stack Developer to join our team. You will help build and support the next generation of Google Sheets, Excel, and Microsoft 365 add-ins used by customers around the world — and you will play a key role in embedding AI into the core of everything we ship.

We are at an inflection point. Across our entire product line, we are actively integrating AI capabilities — from intelligent query generation and natural language data interactions to AI-assisted workflows that make our tools dramatically more powerful for CRM users. This is not a future roadmap item. It is happening now, and the person we hire will be central to it.

What You Will Do

Work across the full stack to build scalable, high-performance distributed systems that deliver excellent user experiences and drive business growth
Develop new features and infrastructure in response to evolving product and business needs
Lead and contribute to our AI integration initiative — designing and building AI-powered features across our product suite, including natural language interfaces, LLM-backed automation, and intelligent data handling capabilities
Take ownership of projects — from concept and design to deployment and iteration
Ensure application performance, reliability, and scalability, maintaining high standards for code quality and architecture
Contribute within an Agile environment, following best practices and continuously improving your skills
Primarily work with JavaScript (ECMAScript 2025+), TypeScript, Node.js, React, and MySQL
Collaborate with a distributed team across time zones using Slack, Jira, and audio/video calls
Actively leverage AI coding tools — including Claude Code and OpenAI Codex — to accelerate development, automate repetitive tasks, and raise the quality bar across the codebase
Stay current with the AI landscape and bring new ideas, tools, and approaches to the team proactively

What You Will Bring

6+ years of experience in a similar full stack role (startup/product experience is a strong plus)
Strong expertise in JavaScript (ECMAScript 2025+), TypeScript, Node.js, React, and MySQL
Experience with modern UI frameworks (e.g., Fluent UI, MobX)
Familiarity with AWS services (e.g., Lambda, DynamoDB)
Hands-on experience with building AI-powered product features — integrating LLM APIs, designing prompts for production use, and shipping AI capabilities to real users
Hands-on experience with AI-assisted development tools, including Claude Code and OpenAI Codex, and the ability to integrate them effectively into day-to-day engineering workflows
Deep, genuine interest in the AI space — you follow model releases, read research updates, track the competitive landscape, and regularly experiment with emerging tools
A strong point of view on how AI is reshaping software development and SaaS products, with the drive to bring that perspective to bear at Xappex
The ability to translate AI capabilities into concrete product value — you can look at what LLMs can do today and immediately see how to make our users’ lives better
Bachelor’s degree in Computer Science, Engineering, IT, or a related field
Fluency in English and Belarusian, or Russian
A proactive, accountable problem-solver

The AI-Forward Mindset We're Looking For

AI is not a feature we are bolting on — it is becoming the backbone of how our products work and how our team operates. We are integrating AI across our entire product line: XL-Connector 365, G-Connector, Enabler4Sheets, and beyond. That means natural language querying of CRM data, AI-assisted data mapping, intelligent error handling, and much more on the roadmap.

We want someone who doesn’t just tolerate AI tools — they are energized by them. You know the difference between GPT-4o and Claude Sonnet and when to use each. You’ve shipped something real using an LLM API, not just tinkered in a playground. You have opinions about prompt engineering, context windows, RAG, and agentic workflows — formed through hands-on experience, not just headlines. You follow Anthropic, OpenAI, Google DeepMind, and the open-source ecosystem closely, because you genuinely find it fascinating.

At Xappex, you will have real influence over how AI shapes our products for years to come. If you want to work somewhere that is actively building the future of AI-powered productivity tools — not planning to someday — this is the role.

Why Join Xappex

Work on products used by hundreds of thousands of customers worldwide
Be at the center of our AI transformation — this is a rare opportunity to shape how AI gets built into a mature, widely-used product suite from the ground up
Be part of a lean, experienced, and collaborative team where your work has direct, visible impact
Opportunity to own projects end-to-end — build, own, ship, and see your work in the hands of real users fast
We actively invest in AI tooling, research, and experimentation — you will be encouraged and supported to stay at the cutting edge
Flexible, remote, friendly work environment

About Xappex

Xappex is a software developer that helps CRM teams manage, automate and report on data faster and more efficiently.